PSI - Issue 57

David Mellé et al. / Procedia Structural Integrity 57 (2024) 61–72

71

David Melle´ / Structural Integrity Procedia 00 (2023) 000–000 11 surface features were extracted and quantified using the Murakami’s √ area parameter and their depth. The surface scans were analyzed to determine the SCF and the stress intensity factor associated with each feature. The killer feature, identified from SEM observations of the failure surfaces, was compared to killer-feature predicted from the scanned population using di ff erent methodologies (largest size, largest depth, highest SCF, highest DK). The total scanned population and killer-feature were plotted on a Kitagawa-Takahashi diagram. It is concluded that: • The scatter associated with the fatigue strength is high. This is shown by the gray band in the Kitagawa Takahashi diagram (Figure 11) which was identified using the El-Haddad and Topper model fitted to the killer features, identified by SEM observation of the failure surfaces. • None of the methods or indicators investigated were su ffi cient to consistently identify the killer-feature from the population (i.e. the largest defect size, the largest depth, the highest SCF, the highest ∆ K ). • The proposed methodology, in which surface scans are used to try to estimate the fatigue strength prior to testing, by identifying the killer surface feature, does not work, at least for this material. It is proposed that this is because the fatigue strength (and its scatter) are not only controlled by the killer-feature, but also by the variation in the inherent strength of the material, or the microstructure, surrounding each individual defect.

Acknowledgements

The authors would like to acknowledge Safran Tech research center members that contributes to this work. They also want to aknowledge people from Fusia, Ineosurf and Mistras group for their help in fabrication, surface treatment and machining of the coupons.

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