Fatigue strength characterization of Al-Si cast material incorporating statistical size effect

Aigner, Roman; Leitner, Martin; Stoschka, Michael

doi:10.1051/matecconf/201816514002

Cited by 15 publications

(21 citation statements)

References 17 publications

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“…Furthermore, to characterize not only the fracture-initiating defects by means of fractography, selected specimens are investigated non-destructively with X-ray computed tomography (XCT). This methodology supports the holistic characterization of the defect population respectively its spatial extent and is further described in [22,48]. Figures 9 and 10 show a fracture surface with a crack origin at a micro pore.…”

Section: Fatigue Testssupporting

confidence: 73%

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Application of a area -Approach for Fatigue Assessment of Cast Aluminum Alloys at Elevated Temperature

Aigner

Garb

Leitner

et al. 2018

Metals

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This paper contributes to the effect of elevated temperature on the fatigue strength of common aluminum cast alloys EN AC-46200 and EN AC-45500. The examination covers both static as well as cyclic fatigue investigations to study the damage mechanism of the as-cast and post-heat-treated alloys. The investigated fracture surfaces suggest a change in crack origin at elevated temperature of 150 ∘ C. At room temperature, most fatigue tests reveal shrinkage-based micro pores as their crack initiation, whereas large slipping areas occur at elevated temperature. Finally, a modified a r e a -based fatigue strength model for elevated temperatures is proposed. The original a r e a model was developed by Murakami and uses the square root of the projected area of fatigue fracture-initiating defects to correlate with the fatigue strength at room temperature. The adopted concept reveals a proper fit for the fatigue assessment of cast Al-Si materials at elevated temperatures; in detail, the slope of the original model according to Murakami should be decreased at higher temperatures as the spatial extent of casting imperfections becomes less dominant at elevated temperatures. This goes along with the increased long crack threshold at higher operating temperature conditions.

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Section: Fatigue Testssupporting

confidence: 73%

“…The tests are performed until a total number of 1×10 7 load cycles, because preliminary studies showed defect correlated specimen failure in the HCF region between 1×10 6 and 1×10 7 load cycles, see [3,48,49]. All evaluated S/N-curves are displayed including the 10 and 90 % probability of survival scatter band.…”

Section: Fatigue Testsmentioning

confidence: 99%

Application of a area -Approach for Fatigue Assessment of Cast Aluminum Alloys at Elevated Temperature

Aigner

Garb

Leitner

et al. 2018

Metals

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“…Amongst others, the effective projected area of the most critical defect perpendicular to the load direction as well as the minimal and maximal distance to the surface are investigated by means of scanning-electron and digital optical microscopy. Further information about this methodology is given in [34]. Subsequently, the relevant geometrical characteristics, such as the equivalent circle diameter deq, are derived (see Equation (3)).…”

Section: Resultsmentioning

confidence: 99%

“…The coefficient C1 is proposed to be 1.56 for interior subsurface defects, and 1.43 for surface defects [33]. Hence, surface intersecting defects are considered to be more fatigue-sensitive, even in the presence of larger interior defects, which is in line with preliminary studies [34,35]. Additionally, the Vickers hardness (HV) of the assessed material is used as a base material strength parameter [36,37].…”

Section: Introductionmentioning

confidence: 94%

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

et al. 2018

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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.

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“…Since a preliminary study in [56] revealed that the area parameter correlates well with the stress field around the inhomogeneity, this parameter is further utilized in this work for the estimation of defect sizes. The defect size measurement methodology invoked in this work is in detail described in [57,58,59]. According to investigations in [60,61], the statistical distribution of defect sizes can be characterized by the limiting extreme value distribution of the Lognormal (LN) distribution, namely the Gumbel or Extreme Value type one distribution (EV) [62,63].…”

Section: Introductionmentioning

confidence: 99%

On the Statistical Size Effect of Cast Aluminium

et al. 2019

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Manufacturing process based imperfections can reduce the theoretical fatigue strength since they can be considered as pre-existent microcracks. The statistical distribution of fatigue fracture initiating defect sizes also varies with the highly-stressed volume, since the probability of a larger highly-stressed volume to inherit a potentially critical defect is elevated. This fact is widely known by the scientific community as the statistical size effect. The assessment of this effect within this paper is based on the statistical distribution of defect sizes in a reference volume V 0 compared to an arbitrary enlarged volume V α . By implementation of the crack resistance curve in the Kitagawa–Takahashi diagram, a fatigue assessment model, based on the volume-dependent probability of occurrence of inhomogeneities, is set up, leading to a multidimensional fatigue assessment map. It is shown that state-of-the-art methodologies for the evaluation of the statistical size effect can lead to noticeable over-sizing in fatigue design of approximately 10 % . On the other hand, the presented approach, which links the statistically based distribution of defect sizes in an arbitrary highly-stressed volume to a crack-resistant dependent Kitagawa–Takahashi diagram leads to a more accurate fatigue design with a maximal conservative deviation of 5 % to the experimental validation data. Therefore, the introduced fatigue assessment map improves fatigue design considering the statistical size effect of lightweight aluminium cast alloys.

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Fatigue strength characterization of Al-Si cast material incorporating statistical size effect

Cited by 15 publications

References 17 publications

Application of a area -Approach for Fatigue Assessment of Cast Aluminum Alloys at Elevated Temperature

Application of a area -Approach for Fatigue Assessment of Cast Aluminum Alloys at Elevated Temperature

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

On the Statistical Size Effect of Cast Aluminium

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