Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Very high cycle fatigue of duplex stainless steels and stress intensity calculations
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics. (Materials Engineering Group)ORCID iD: 0000-0003-1672-1235
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 [en]
Very high cycle fatigue, duplex stainless steel, ultrasonic fatigue testing, distributed dislocation dipole technique
National Category
Mechanical Engineering
Research subject
Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-34591ISBN: 978-91-7063-610-3 (print)OAI: oai:DiVA.org:kau-34591DiVA: diva2:762810
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: 2017-12-06Bibliographically approved
List of papers
1. Review of VHCF studies, short crack models and theory of vibrations
Open this publication in new window or tab >>Review of VHCF studies, short crack models and theory of vibrations
(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
Very cycle high fatigue, crack initiation, short cracks, vibration, damping
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kau:diva-34634 (URN)
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: 2017-12-06
2. Fatigue initiation and strength of duplex stainless steel strip specimens in the very high cycle fatigue regime
Open this publication in new window or tab >>Fatigue initiation and strength of duplex stainless steel strip specimens in the very high cycle fatigue regime
2014 (English)In: Very high cycle fatigue 6 (VHCF6), 2014Conference paper, Published paper (Refereed)
Abstract [en]

Fatigue studies of cold-rolled duplex stainless strip steel were performed in the very high cycle fatigue life region. The duplex austenitic-ferritic microstructure gives this grade a combination of high mechanical strength and high corrosion resistance. Fatigue properties of thin steel strips are particular due to cold rolling introducing a very fine microstructure. Crack initiation and fatigue strength are controlled by steel microstructure and alloying. The initiation and growth of the very short initial fatigue crack in very high cycle fatigue are unclear and subject to different descriptions. Fatigue test data of thin strip specimens at very high fatigue lives are scarce due to testing difficulties. For practical reasons testing must be performed at ultrasound test frequencies which involves fixturing problems. A test setup including the load chain ultrasonic horn, fixture and specimen was designed for resonance with a horse-shoe design of a screw fixture. The design of the horse-shoe fixture and the specimens along with FEM calculation of eigenfrequency are presented. Fatigue testing was performed at 20 kHz in R=-1 conditions up to fatigue life of 107 to 5*109 cycles. Fatigue strength was tested and crack initiation was studied on the fracture surface using FEG-SEM at the initiation site.

Keyword
Very high cycle fatigue, initiation, ultrasonic fatigue testing, strip specimen
National Category
Other Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-34633 (URN)
Conference
6th International conference on very high cycle fatigue (VHCF6), Chengdu, China
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: 2017-12-06Bibliographically approved
3. Fatigue strength, crack initiation, and localized plastic fatigue damage in VHCF of duplex stainless steels
Open this publication in new window or tab >>Fatigue strength, crack initiation, and localized plastic fatigue damage in VHCF of duplex stainless steels
Show others...
2016 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, no 7, 899-910 p.Article in journal (Refereed) Published
Abstract [en]

The fatigue strength of two-duplex stainless steel grades, 2304 SRG and LDX 2101, with austenitic–ferritic microstructure is tested using ultrasonic fatigue testing equipment operating at 20 kHz. The testing is conducted in tension-compression mode with the load ratio R=-1. The fatigue strength is evaluated at 107, 108, and 109 load cycles and the estimates of fatigue strength are higher for the LDX 2101 grade. The fatigue crack initiation mechanisms are analyzed using a scanning electron microscope. The fatigue cracks, in all cases, appear to initiate due to accumulation of plastic fatigue damage at the surface. In the 2304 SRG grade, accumulation of fatigue damage occurs at the external surface of fatigued specimens in the form of extrusions at the grain/phase boundaries and in the form of individual slip lines in the austenite phase. Meanwhile, in the LDX 2101 grade accumulation of plastic fatigue damage in the form of extrusions and intrusions occurs mainly within the ferrite grain. When the crack is microstructurally short, the crack growth appears to be crystallographic in nature and the crack appears to change its direction propagating from one grain into another.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2016
Keyword
duplex stainless steel; ultrasonic fatigue testing; plastic fatigue damage; very high cycle fatigue; crystallographic crack growth
National Category
Metallurgy and Metallic Materials
Research subject
Materials Engineering; Mechanical Engineering
Identifiers
urn:nbn:se:kau:diva-38693 (URN)10.1002/srin.201500263 (DOI)000385610500010 ()
Projects
Very High Cycle Fatigue of Stainless Steels - an unknown life
Funder
Knowledge Foundation
Available from: 2015-11-23 Created: 2015-11-23 Last updated: 2017-12-06Bibliographically approved
4. Development of a distributed dislocation dipole technique for the analysis of multiple straight, kinked and branched cracks in an elastic half-plane
Open this publication in new window or tab >>Development of a distributed dislocation dipole technique for the analysis of multiple straight, kinked and branched cracks in an elastic half-plane
2014 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, 2878-2892 p.Article in journal (Refereed) Published
Abstract [en]

A distributed dislocation dipole technique for the analysis of multiple straight, kinked and branched cracks in an elastic half plane has been developed. The dipole density distribution is represented with a weighted Jacobi polynomial expansion where the weight function captures the asymptotic behaviour at each end of the crack. To allow for opening and sliding at crack kinking and branching the dipole density representation contains conditional extra terms which fulfil the asymptotic behaviour at each endpoint. Several test cases involving straight, kinked and branched cracks have been analysed, and the results suggest that the accuracy of the method is within 1% provided that Jacobi polynomial expansions up to at least the sixth order are used. Adopting even higher order Jacobi polynomials yields improved accuracy. The method is compared to a simplified procedure suggested in the literature where stress singularities associated with corners at kinking or branching are neglected in the representation for the dipole density distribution. The comparison suggests that both procedures work, but that the current procedure is superior, in as much as the same accuracy is reached using substantially lower order polynomial expansions.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Cracks, Dislocation dipoles, stress intensity factors, Singular integral equations
National Category
Other Mechanical Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-34744 (URN)10.1016/j.ijsolstr.2014.04.011 (DOI)000338005200013 ()
Projects
Very high cycle fatigue of stainless steels- an unknown life
Funder
Knowledge Foundation
Available from: 2014-12-09 Created: 2014-12-09 Last updated: 2017-12-06Bibliographically approved

Open Access in DiVA

fulltext(2576 kB)546 downloads
File information
File name FULLTEXT01.pdfFile size 2576 kBChecksum SHA-512
5bf463e84c1c2792fb9d27c1b5b4e9a790a78ae9145579df58e7b8175eaf9b66f6f0e37cd875df65dc47c724e674acff3fa5d8f9f7aa2ab09a0ab0193460808e
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Tofique, Muhammad Waqas
By organisation
Department of Engineering and Physics
Mechanical Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 546 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 360 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf