PSI - Issue 66

Venanzio Giannella et al. / Procedia Structural Integrity 66 (2024) 71–81 Venanzio Giannella et al./ Structural Integrity Procedia 00 (2025) 000 – 000

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Δ F = 42.75 kN R = 0.05

K I calculation path

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Transverse K I calculation path

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Crack length, a [mm]

Fig. 8. Trend of the mode I Stress Intensity Factor (SIF) K I evaluated by FRANC 3D along the paths defined inside the figure, as a function of the crack length a. The calculation has been performed by applying a load range ΔF = 42.75 kN with a nominal load ratio R = 0.05.

5. Conclusions Steel welded joint geometries used in off-road vehicles and consisted of a pipe penetrating a plate by means of four intermittent transverse or longitudinal fillet welds, have been fatigue tested under axial loading in a previous work. The PSM was able to properly estimate the experimental crack initiation sites, i.e. the tube-side weld toe and the plate side weld toe for the transverse and the longitudinal joints, respectively. However, the PSM estimated the fatigue life of transverse joints on the safe side, while it accurately estimated the fatigue life of longitudinal joints. This result was attributed to the exceptionally long crack propagation phase which occurred in the transverse joints and that was inherently excluded in the PSM approach. In the present work, the crack propagation phase of both transverse and longitudinal joints has been furtherly investigated by taking advantage of FE analyses performed in Abaqus® coupled with FRANC3D®. To this aim, a semi-circular crack having depth a i = 0.1 mm has been introduced in the FE models in the experimental crack initiation locations; then, its propagation has been simulated up to the final failure. The numerical results allowed to justify the different behaviour of the considered joints, since the crack driving force resulted almost constant during the crack propagation in transverse joints, therefore leading to reduced crack-growth rates that, according to Paris law, generates an extremely long crack propagation phase. On the other hand, K I resulted a monotonically increasing function of the crack length in longitudinal joints, hence implying a considerably shorter crack propagation phase. A future development of this work will involve the fatigue life predictions for both materials (S355 steel and 25MnCr6 Q&T), by extracting SENB specimens from the tested joints. References Baumgartner J, Schmidt H, Ince E, et al (2015) Fatigue assessment of welded joints using stress averaging and critical distance approaches. Weld World 59:731 – 742. https://doi.org/10.1007/s40194-015-0248-x Campagnolo A, Roveda I, Meneghetti G (2019) The Peak Stress Method combined with 3D finite element models to assess the fatigue strength of complex welded structures. Procedia Struct Integr 19:617 – 626. https://doi.org/10.1016/j.prostr.2019.12.067