Issue 78

A. Sancak et alii, Fracture and Structural Integrity, 78 (2026) 186-206; DOI: 10.3221/IGF-ESIS.78.11

Effect of notch timing The influence of notch timing was evaluated using specimens exposed to seawater for 30 days. Two conditions were compared: specimens notched after corrosion exposure and specimens notched before corrosion exposure. In the first condition, the specimens were immersed in the unnotched state and the Charpy V-notch was machined after corrosion exposure. In the second condition, the notch was introduced before immersion, so that the notch root was directly exposed to seawater during the entire corrosion period. At 0 °C, the specimens notched after corrosion exposure had an average absorbed energy of 10.62 ± 5.55 J. In contrast, the pre-notched specimens exposed to seawater for the same duration exhibited an average absorbed energy of 15.52 ± 10.19 J. Although this mean value is higher than that of the post-corrosion-notched condition, the pre-notched group showed very large scatter. The individual absorbed energies were 14.63, 26.13 and 5.80 J. Therefore, the higher mean value of the pre-notched group at 0 °C should not be interpreted as a beneficial effect of pre-notching. The large variation among the individual specimens shows that the mean response was strongly influenced by specimen-to-specimen variability. At 23 °C, the opposite tendency was observed. The 30-day seawater specimens notched after corrosion exposure exhibited an average absorbed energy of 19.90 ± 10.00 J, whereas the pre-notched specimens tested at 23 °C showed an average absorbed energy of 15.30 ± 3.07 J. Compared with the uncorroded 23 °C reference value of 53.90 J, these values correspond to reductions of approximately 63.1% and 71.6%, respectively. At 23 °C, the pre-notched specimens exhibited a lower mean absorbed energy than the specimens notched after corrosion exposure. This tendency was opposite to that observed at 0 °C, indicating that the notch-timing response depended on the test temperature and the local specimen condition. Overall, the two notch-timing conditions exhibited different mean absorbed energies and levels of scatter, but the direction of the trend was not consistent at 0 and 23 °C. Direct exposure of the notch root to seawater may alter the local surface condition near the notch root. However, the absorbed impact energy was also influenced by test temperature, local material condition and specimen-to-specimen variability. Therefore, notch timing should be considered together with these parameters rather than as an independent controlling factor. Corrosion mass loss and corrosion rate The calculated mass loss and corrosion rate values are summarized in Tab. 5.

Corrosion rate, mm/year

Mass loss Specimen 1, g

Mass loss Specimen 2, g

Mass loss Specimen 3, g

Mean mass loss ± SD, g 0.100 ± 0.017 0.070 ± 0.010 0.213 ± 0.040 0.147 ± 0.006 0.177 ± 0.015 0.193 ± 0.012 0.123 ± 0.025

Group

5 6 7 8 9

0.12 0.08 0.17 0.15 0.16 0.20 0.15

0.09 0.06 0.22 0.14 0.19 0.18 0.10

0.09 0.07 0.25 0.15 0.18 0.20 0.12

0.194 0.136 0.138 0.095 0.114 0.125

10 11

0.080 Table 5: Corrosion mass loss and calculated corrosion rate of corrosion-exposed specimens. Note: Corrosion rates were calculated according to ASTM G31-21 [34] using A = 24 cm², ρ = 7.85 g/cm³, t = 240 h for 10 days and t = 720 h for 30 days. The corrosion products were not removed before Charpy impact testing. After testing, corrosion products were removed using P500C abrasive paper and the mass loss was determined from the difference between the initial and final specimen masses. Seawater produced higher mean mass loss than substitute seawater at both exposure durations. After 10 days, the average mass loss was 0.100 g in seawater and 0.070 g in substitute seawater. After 30 days, for specimens notched after corrosion exposure and tested at 0 °C, the corresponding values were 0.213 g and 0.147 g, respectively. Thus, seawater produced approximately 43% higher mean mass loss after 10 days and approximately 45% higher mean mass loss after 30 days compared with substitute seawater. The corrosion rate values were higher for the 10-day groups than for some of the 30-day groups because corrosion rate is normalized by exposure time. This suggests that the initial corrosion stage may have proceeded relatively rapidly, whereas the subsequent development of corrosion products may have modified the corrosion kinetics. Therefore, total mass loss

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