PSI - Issue 75

Kevin Mouradian et al. / Procedia Structural Integrity 75 (2025) 616–624 Kevin Mouradian et al. / Structural Integrity Procedia (2025)

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presents the testing parameters for each specimen, including the applied stress amplitude Δ σ and the corresponding number of cycles to rupture N . Notably, failure consistently occurred near the weld toe, which sometimes coincides with imperfections such as undercuts. Specimens from series BW_TYPE and BW_UND were analyzed individually to evaluate the effect of weld imperfections on the fatigue strength. The statistical evaluation method (ECCS 2018) was employed to determine the characteristic fatigue strength Δ σ c at two million cycles. The lower prediction bound, with a 95% probability of survival was applied, as defined in prEN 1990 (CEN 2021) . The slope of the S‑N curve was fixed at m = 3.

Table 5. Summary of fatigue test results

Final QL ISO 5817

Final QL annex B

Stress amplitude Δ σ [N/mm²]

Cycles to rupture N 344 809 585 171 480 892 619 409 257 656 410 281 106 701 64 818 280 593 99 232 5 000 000 * 2 867 595

Failure location

Stress ratio

Specimen

TYPE_1 TYPE_2 TYPE_3 TYPE_4 TYPE_5 TYPE_6 UND_1 UND_2 UND_3 UND_4 UND_5 UND_6

D B D D

Weld toe Weld toe Weld toe Weld toe Weld toe Weld toe Weld toe Weld toe Weld toe Weld toe Weld toe

0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10

180.4 180.2 210.2 165.2 165.2 210.2 165.2 165.2 210.2 210.2 165.2 210.3

C63

No failure (runout)

B

D

The BW_TYPE specimens were initially intended to serve as reference specimens corresponding to quality level B. However, only two specimens fulfilled the corresponding requirements, while the rest exhibited lower quality levels, including D and

Fig. 4 illustrates fatigue test results for BW_TYPE and BW_UND specimens, along with data from the “ filtered database ”.