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
In-situ SEM/EBSD Study of Deformation adn Fracture Behaviour of Flake Cast Iron
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Cast irons’ position as an important engineering material is un-disputed. They are widely used in many important industrial applications such as the automotives and workshop machinery. Nevertheless, fracture mechanisms in cast irons are not fully understood. In this study the fracture path and non-linear elastic behaviour of a fully pearlitic flake cast iron under uniaxial tensile loading have been investigated in a Scanning Electron Microscope (SEM) equipped with an Electron Backscattering Diffraction (EBSD) detector. The tensile load was applied via a specially made sample stage. Under uniaxial tensile loading the graphite flakes act as notches or cracks and therefore the fracture process starts at one or many graphite tips. The crack can propagate in many different ways, at the graphite and matrix interface, through the graphite, at the interface between cementite and ferrite or through the pearlitic grains. At the point where the stress strain curve deviates from its linear path plastic deformation at graphite tips can be noticed. Interface cracking between graphite and the matrix also starts at this point.

Place, publisher, year, edition, pages
2013. p. 1-9
Keywords [en]
high-temperature, ageing, toughness, austenitic stainless steel, nickel base alloy
National Category
Engineering and Technology Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-95430OAI: oai:DiVA.org:liu-95430DiVA, id: diva2:635235
Conference
13th International Conference on Fracture ICF13, June 16-21, Beijing, China.
Available from: 2013-07-03 Created: 2013-07-03 Last updated: 2018-08-30
In thesis
1. Residual Stresses and Fatigue of Shot Peened Cast Iron
Open this publication in new window or tab >>Residual Stresses and Fatigue of Shot Peened Cast Iron
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The complex geometry of cylinder head in heavy-duty diesel engine makes grey cast iron or compact graphite iron a perfect material choice due to its castability, thermal conductivity and damping capacity. To increase the efficiency of the engine, the fatigue property of the material needs to be improved. Shot peening is often used to increase the fatigue strength of components. The benefits are associated with the compressive stresses induced and with surface hardening. In this research project, these effects on grey and compact iron have been analyzed for different shot peening parameters using XRD, SEM and fatigue testing methods. The ultimate aim of the project is to increase the fatigue strength of cast irons by optimization of residual stresses.

The XRD measurements and SEM examinations revealed that the shot peening parameters including shot size and peening intensity had significant influences on the resulted residual stresses and strain hardening while changing the coverage made little difference. Also differences in the peening results between the two materials were observed, which were ascribed to an effect of the different graphite morphology. Nevertheless, a residual stress profile similar to the one general considered to improve the fatigue strength in steels could be obtained in both grey and compact iron after shot peening.

The axial fatigue testing with R=-1 on the grey iron showed that peening using large shot size and high peening intensity (heavy shot peening) resulted in a fatigue strength reduction of 15-20% in comparison with the mechanically polished surface. The negative effects are likely related to surface damage and relatively high tensile residual stresses in subsurface induced by the heavy peening. Grey cast iron has low ductility in tension and therefore tensile residual stresses may promote multiple cracking and crack networking during cyclic loading.

Shot peening using much smaller shots and lower intensity (gentle shot peening) which resulted in a much smaller residual stress field gave no significant changes in fatigue strength. However, a short time annealing at 285°C of specimens being gently shot peened increased the fatigue strength roughly by 10%. The improvement could be an effect of precipitates formed due to the heat treatment, which lock the dislocation movement under cyclic loading.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. p. 45
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1622
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-99842 (URN)10.3384/lic.diva-99842 (DOI)LiU-TEK-LIC-2013:56 (Local ID)978-91-7519-501-8 (ISBN)LiU-TEK-LIC-2013:56 (Archive number)LiU-TEK-LIC-2013:56 (OAI)
Presentation
2013-10-24, ACAS, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-10-21 Created: 2013-10-21 Last updated: 2013-11-12Bibliographically approved
2. Residual stresses, fatigue and deformation in cast iron
Open this publication in new window or tab >>Residual stresses, fatigue and deformation in cast iron
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The complex geometry of cylinder heads in heavy-duty diesel engines makes grey iron or compact graphite iron a preferred material choice due to its price, castability, thermal conductivity and damping capacity. Today’s strict emission laws have increased the demands on engine performance and engine efficiency. This means that material properties such as fatigue resistance need to be improved. Shot peening is often used to improve the fatigue resistance of components and the benefits of shot peening are associated with the induced compressive surface stresses and surface hardening. How different shot peening parameters can affect fatigue strength of grey and compact graphite iron has been investigated within the project underlying this thesis. To do this, X-ray diffraction (XRD) was utilized for residual stress measurements, scanning electron microscopy (SEM) for microstructural characterizations and mechanical fatigue testing for mechanical quantifications. The ultimate aim of this work has been to increase the fatigue resistance of cast iron by residual stress optimization.

XRD measurements and SEM examinations revealed that the shot peening parameters shot size and peening intensity significantly influence residual stresses and surface deformation. Residual stress profiles, similar to the one general considered to improve the fatigue strength in steels, were obtained for both grey and compact graphite iron. Uniaxial push-pull fatigue testing on grey iron with these shot peening parameters reduced the fatigue strength with 15–20 %. The negative effect is likely related to surface damage associated with over peening and relatively high subsurface tensile residual stresses. With very gentle shot peening parameters, the uniaxial fatigue strength were unaltered from the base material but when subjected to bending fatigue an increase in fatigue strength were observed. An alternative way to increase the fatigue strength was to conduct a 30 min annealing heat treatment at 285 XC which increased the fatigue strength by almost 10 % in uniaxial loading. The improvement could be an effect of favourable precipitates forming during the annealing, which could hinder dislocation movement during fatigue.

Measuring residual stresses using XRD and the sin2 -method demands accurate X-ray elastic constants (XEC) for meticulous stress analysis. The XEC referred to as 1~2s2 should therefore always be calibrated for the specific material used. The experiments conducted revealed that the XEC value is independent of the testing method used in this work. A small correction from the theoretical value should be applied when the material contains small amounts of residual stresses. The amount of residual stresses has a great impact on the XEC and thus on the stress analysis. Concluding that proper analysis of residual stresses in cast iron is not straight forward.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. p. 44
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1908
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-150783 (URN)10.3384/diss.diva-150783 (DOI)9789176853580 (ISBN)
Public defence
2018-09-28, ACAS, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2018-08-30 Created: 2018-08-30 Last updated: 2018-09-21Bibliographically approved

Open Access in DiVA

No full text in DiVA

Search in DiVA

By author/editor
Lundberg, MattiasCalmunger, MattiasPeng, Ru
By organisation
Engineering MaterialsThe Institute of Technology
Engineering and TechnologyMaterials Engineering

Search outside of DiVA

GoogleGoogle Scholar

urn-nbn

Altmetric score

urn-nbn
Total: 222 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