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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(a)

last increment

Front view

Crack propagation direction

(b)

Fig. 7. (a) Crack propagation steps as obtained from FE simulations of the transverse joint geometry. (b) Comparison with the experimental crack propagation path and the fracture surface, as observed in Ref. (Pelizzari et al. 2024).

Finally, the crack propagation simulations have allowed to calculate the crack driving force K I as a function of the crack length a along the propagation paths defined in Figures 6a and 7a. Such results have been reported in Figure 8 both for the longitudinal and the transverse joints, again with reference to a load range ΔF = 42.75 kN and a load ratio R = 0.05. It can be observed from Figure 8 that the crack driving force calculated for the transverse joint is nearly constant during crack-growth, which is in agreement with the qualitative discussion reported in Section 3 and in Ref. (Pelizzari et al. 2024). Indeed, it has been observed that during crack propagation, the crack length a increases while the stress range decreases due to a tube stiffness drop. An almost constant K I value is responsible of the extremely long crack propagation phase observed in transverse joints. Conversely, the crack driving force calculated for the longitudinal joint exhibits a monotonically increasing trend, which is typical in crack propagation problems (Giannella 2021; Giannella et al. 2021, 2022b). This is in agreement with the experimental results which did not show a long crack propagation phase.