PSI - Issue 38

Isabel Huther et al. / Procedia Structural Integrity 38 (2022) 466–476 Huther et al./ Structural Integrity Procedia 00 (2021) 000 – 000

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7. Conclusions and further work Welded assemblies with longitudinal stiffeners were performed by a member of the Crane industry committee according to a protocol established with the manufacturers. Residual stress analyses have shown a significant relaxation of residual stresses after preloading, thereby improving fatigue performance. The interrupted fatigue tests exhibited a stability of the residual stresses in time. All the fatigue results of the different campaigns were used to draw probabilized SN curves to evaluate a Fatigue class for each configuration. A FAT63 corresponding to detail class 523 of the IIW recommendation [4] was found for the reference specimens and for a preload of 1Re, and a class 74/99 was found for the specimens with local preloads at the weld toe of 1.25Re and 1.56Re. The perspectives of this study are to: - Verify that on welded structure transmitting effort, a preload does also lead to a beneficial effect demonstrated on a weld with stiffener. - To verify if the gain is superior for a HLE steel: i.e. that the use of a material with superior mechanical tensile properties leads to a delay in the crack initiation phase. - Check if it is possible to predict by elasto-plastic modeling the effect of this preload on the number of cycles. New test campaigns are scheduled to investigate these 3 further works in a large collaborative research program called “PTT SoudFat”. References [1] ASTM A391 / A391M-07. Standard Specification for Grade 80 Alloy Steel Chain. s.l. : ASTM, 2012. ASTM A391 / A391M [2] DNVGL-RP-0005:2014-06, RP-C203: Fatigue design of offshore steel structures [3] EN 15305, Non-destructive Testing - Test Method for Residual Stress analysis by X-ray Diffraction [4] Hobbacher, A. F, Recommendations for Fatigue Design of Welded Joints and Components, Second Edition, IIW Collection, Springer 2016 - IIW-2259-15 [5] Lefebvre, F., Effet d'une charge d'épreuve sur le comportement en fatigue d'une structure soudée -V1, Cetim report n°225653, juin 2019. [6] Lefebvre, F., Effet d'une charge d'épreuve sur le comportement en fatigue d'une structure soudée – V2, Cetim report n°242539, décembre 2020. [7] F. Lefebvre, C. Peyrac, G. Elbel, C. Revilla-Gomez, C. Verdu et J.-Y. Buffière, «HFMI: understanding the mechanisms for fatigue life improvement and repair of welded structures» vol. 61, n° %1,4,789-799 Springer Berlin, 2017. [8] Nagase Y., Suzuki S., (1992), On the Decrease of Fatigue Limit Due to Small Prestrain, J Eng Mater Tech, Vol. 114 / 317 [9] DNVGL-RP-C208 Determination of Structural Capacity by Non-linear Finite Element Analysis Methods-DNVGL (2021)