PSI - Issue 57

444 Lorenzo Bercelli et al. / Procedia Structural Integrity 57 (2024) 437–444 8 L. Bercelli, C. Guellec, B. Levieil, C. Doudard, F. Bridier, S. Calloch / Structural Integrity Procedia 00 (2019) 000 – 000 5. Conclusion The effect of the stress ratio in the vicinity of the weld toe on the fatigue life of welded T-joints was investigated in this study. It was shown, by the monitoring of fatigue cracks at the weld toe via TSA, that the applied load ratio has a strong effect on the crack propagation speed. This effect is attributed to the occurrence of a crack closure phenomenon for = 10 which is detected in the temperature signal close to cracks. A signal processing method was proposed in order to measure the extent of the crack closure in the different testing configurations, through the definition of the crack opening rate , used to determine the effective stress range Δ = Δ . Introducing this effective stress range in a LEFM based approach, fatigue lives are estimated and compared to experimental results. The consideration of the crack opening rate estimated from infrared data significantly improves fatigue forecasts. These results give good confidence in the proposed approach based on the definition of an effective stress range Δ , which dependence to the nominal loading can be established via infrared observation of crack closure or via the unification of crack propagation kinetics at different loading ratios , as proposed in Bercelli et al. (2023). Moreover, the present work shows the great potential of the proposed infrared technique, allowing the in-situ assessment of the crack closure which is closely related to the local stress state near the fatigue crack. This should allow for a finer assessment of the evolution of the local stress state throughout a fatigue test, and could also facilitate the study of variable amplitude loadings. The availability of additional test results, at different load ratios , as well as with different joint thicknesses or other welded-joint configurations, should give even better confidence in this experimental technique. Acknowledgements A part of this study belongs to the “Self - Heating” ANR -Safran-Naval Group research chair (grant no. ANR-20 CHIN-0002), involving Safran Companies, Naval Group, ENSTA Bretagne (IRDL), and Institut Pprime. The authors would also like to thank Direction Géné rale de l’Armement (DGA) for its support. References Alam, M. M., Barsoum, Z., Jonsén, P., Häggblad, H. A., and Kaplan, A. F. H. [2009]. Geometrical aspects of the fatigue behavi our of laser hybrid fillet welds. Proceedings of the Fatigue Design Conference. Barsoum, Z., and Barsoum, I. [2009]. Residual stress effects on fatigue life of welded structures using LEFM. Engineering Failure Analysis, 16(1), 449–467. Bercelli, L., Levieil, B., Malek, B., Bridier, F., and Ezanno, A. [2023]. 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