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Modification of a Defect-Based Fatigue Assessment Model for Al-Si-Cu Cast Alloys

1
Christian Doppler Laboratory for Manufacturing Process based Component Design, Chair of Mechanical Engineering, Montanuniversität Leoben, 8700 Leoben, Austria
2
University of Applied Sciences Upper Austria, 4600 Wels, Austria
3
BMW Motoren GmbH, 4400 Steyr, Austria
*
Author to whom correspondence should be addressed.
Materials 2018, 11(12), 2546; https://doi.org/10.3390/ma11122546
Received: 13 November 2018 / Revised: 4 December 2018 / Accepted: 11 December 2018 / Published: 14 December 2018
(This article belongs to the Special Issue Alloy and Process Development of Light Metals)
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Abstract

Cast parts usually inherit internal defects such as micro shrinkage pores due to the manufacturing process. In order to assess the fatigue behaviour in both finite-life and long-life fatigue regions, this paper scientifically contributes towards a defect-based fatigue design model. Extensive fatigue and fracture mechanical tests were conducted whereby the crack initiating defect size population was fractographically evaluated. Complementary in situ X-ray computed tomography scans before and during fatigue testing enabled an experimental estimation of the lifetime until crack initiation, acting as a significant input for the fatigue model. A commonly applied fatigue assessment approach introduced by Tiryakioglu was modified by incorporating the long crack threshold value, which additionally enabled the assessment of the fatigue strength in the long-life fatigue regime. The presented design concept was validated utilising the fatigue test results, which revealed a sound agreement between the experiments and the model. Only a minor deviation of up to about five percent in case of long-life fatigue strength and up to about 9% in case of finite-lifetime were determined. Thus, the provided extension of Tiryakioglu’s approach supports a unified fatigue strength assessment of cast aluminium alloys in both the finite- and long-life regimes. View Full-Text
Keywords: aluminium casting; fatigue assessment; defects; statistical distribution; extreme value statistics; computed tomography aluminium casting; fatigue assessment; defects; statistical distribution; extreme value statistics; computed tomography
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Aigner, R.; Leitner, M.; Stoschka, M.; Hannesschläger, C.; Wabro, T.; Ehart, R. Modification of a Defect-Based Fatigue Assessment Model for Al-Si-Cu Cast Alloys. Materials 2018, 11, 2546.

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