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Residual Stresses in Shot Peened Grey and Compact 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.
Volvo Powertrain, Gothenburg, Sweden.
Scania CV AB, Södertälje, Sweden.
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2014 (English)In: HTM Journal of Heat Treatment and Materials, ISSN 1867-2493, Vol. 69, no 1, p. 38-45Article in journal (Refereed) Published
Abstract [en]

Grey cast iron and compacted graphite iron with a pearlitic matrix are investigated in this study after shot peening using twelve unique combinations of parameters, namely shot size, peening intensity and coverage, followed by residual stress measurements and evaluations. Cylindrical test samples were cut out from heavy truck cylinder heads and polished on the top flat surface to decrease effects from cutting. Residual stresses and the affected depth from the different peening conditions varied between −245 MPa to −565 MPa and from 280 μm to 770 μm in depth. Resultant surface compressive stresses decrease with increasing shot size, peening intensity or coverage whereas the affected depth increases with increasing intensity. The increased affected depth is a result from the increased extent and magnitude of plastic deformation. The compacted graphite iron was more affected by shot peening than the grey cast iron, meaning that the same shot peening parameters resulted in both higher compressive stresses and larger deformation depth.

Place, publisher, year, edition, pages
Carl Hanser Verlag GmbH, 2014. Vol. 69, no 1, p. 38-45
Keywords [en]
Residual stress, FWHM, cast iron, shot peening, X-ray diffraction
National Category
Engineering and Technology Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-105158DOI: 10.3139/105.110207Scopus ID: 2-s2.0-84896531682OAI: oai:DiVA.org:liu-105158DiVA, id: diva2:703916
Conference
International Conference on Residual Stresses ICRS9, October 7-9,2012 in Garmisch-Partenkirchen, Germany
Note

Enhanced contribution based upon a presentation at the International Conference on Residual Stresses ICRS9, October 7–9, 2012, in Garmisch-Partenkirchen, Germany

Available from: 2014-03-10 Created: 2014-03-10 Last updated: 2018-08-30Bibliographically approved
In thesis
1. 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

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Lundberg, MattiasPeng, RuJohansson, Sten

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