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

78 8

4. the average crack extension Δa is defined by the user starting from as low as 0.01 mm and up to 1 mm, i.e. a value increasing with the actual crack length. 5. FRANC3D® introduces the new crack front in the FE model, remeshes the model locally. 6. The procedure is repeated from point (1) to (5) until that a stopping criterion is reached, e.g. final failure of the component. Once obtained the SIFs as a function of the crack length a , FRANC3D® applies the Paris law according to Eq. (4) and defines the fatigue life. The procedure described above has been applied to both longitudinal and transverse joints, by applying to the FE model a cyclic load with range ΔF = 42.75 kN and a load ratio R = 0.05. The resulting crack propagation paths have been reported in Figures 6a and 7a for longitudinal and transverse joints, respectively, and compared with the relevant experimental observations (Figures 6b and 7b). Figure 6a shows the crack propagation steps from the initial crack up to the final failure of the longitudinal joint. It can be observed that the initial crack propagates from the plate-side weld toe through the plate and this is in very good agreement with the experimental outcomes both in terms of crack front shapes and crack propagation direction, as highlighted by the comparison of Figure 6a with Figure 6b.

(a)

Crack front

After 65 increments

After 30 increments

After 10 increments

After 40 increments

Crack propagation direction

Front view

(b)

Fig. 6. (a) Crack propagation steps as obtained from FE simulations of the longitudinal joint geometry. (b) Comparison with the experimental crack propagation path and the fracture surface, as observed in Ref. (Pelizzari et al. 2024). Figure 7a shows the last crack propagation step simulated in the transverse joint. The initial crack propagates from the tube-side weld toe through the tube, with crack front shapes and crack propagation direction which resulted also in this case in pretty good agreement with the experimental outcomes reported in Figure 7b.