PSI - Issue 39

Riccardo Cappello et al. / Procedia Structural Integrity 39 (2022) 179–193 Author name / Structural Integrity Procedia 00 (2019) 000–000

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• The combination of TSA and the Least Squares Fitting of the Williams stress series constitutes an effective tool for the crack growth characterization under fatigue loading. In particular, it has been shown that they provide more accurate and reliable measurement of the crack length, compared to the one determined optically via a high-resolution digital camera, and allow the determination of the Paris’ law coefficients. • The thermoelastic second harmonic is a sensitive indicator of the presence of crack closure: this can be associated to a peculiar “signature” in the Second Harmonic map which has the resemblance of a turtle shape in the amplitude maps and a butterfly in the phase map, with a 180° phase shift between the two butterfly wings, and the physical crack tip position placed in the butterfly body. • Both the amplitude and phase signatures of crack closure are able to give a a clear qualitative information about the extension of the contact area between the flanks of the crack. • The presence of an overload and the subsequent compressive stress state affects the shape of both the first harmonic and second harmonic amplitude isopachics. 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