Issue 78

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

summarized in Tab. 6. The values reported in the table represent the average hardness values obtained for the three specimens in each group. The hardness values were generally within a relatively narrow range, mostly between approximately 80 and 85 HRB, except for the substitute seawater 30-day group, which showed a higher average hardness of 91.33 ± 1.15 HRB. However, the hardness results did not reveal extreme deviations that could independently explain the large scatter observed in the Charpy impact energies. For example, the uncorroded room-temperature reference group showed absorbed energies ranging from 22.19 to 78.59 J, while the corresponding hardness values were 79, 85 and 78 HRB. Similarly, the pre-notched seawater group tested at 0 °C showed absorbed energies ranging from 5.80 to 26.13 J, whereas the hardness values were very close, between 83 and 84 HRB. These comparisons indicate that hardness variation was not the dominant factor controlling the scatter in absorbed impact energy. Pearson correlation analysis was performed using the individual hardness and absorbed impact energy values of all eleven experimental groups ( n = 33). A weak negative correlation was obtained between hardness and absorbed impact energy, r = − 0.156, p = 0.387. The corresponding linear fit had a coefficient of determination of R 2 = 0.024. Therefore, no statistically significant linear relationship was detected between hardness and absorbed impact energy. The low R 2 value indicates that hardness accounted for only approximately 2.4% of the variation in absorbed impact energy within the present dataset.

Hardness, HRB Specimen 1

Hardness, HRB Specimen 2

Hardness, HRB Specimen 3

Mean ± SD, HRB 80.67 ± 3.79 80.33 ± 2.08 85.33 ± 3.06 84.00 ± 1.00 80.33 ± 0.58 82.00 ± 2.00 85.33 ± 3.06 91.33 ± 1.15 84.00 ± 2.65 83.67 ± 0.58

Group

1 2 3 4 5 6 7 8 9

79 78 82 84 81 84 86 92 87 84 85

85 82 88 83 80 82 82 92 83 83 83

78 81 86 85 80 80 88 90 82 84 86

10 11

84.67 ± 1.53 Table 6: HRB hardness values of reference and corrosion-exposed specimens.

The substitute seawater 30-day group had the highest average hardness, but its average absorbed energy was only 11.02 ± 1.36 J. Therefore, slightly higher hardness did not correspond to lower absorbed impact energy in the corrosion-exposed condition. The hardness measurements should be interpreted as supporting data: they show that the observed scatter cannot be explained simply by the measured macroscopic hardness differences. Other possible factors, including local material variability and corrosion-related surface condition, should also be considered. The hardness distribution and the relationship

between hardness and absorbed impact energy are shown in Fig. 7. Stereomicroscope observations of fracture surfaces and fracture paths

Stereomicroscope observations were performed to evaluate the macroscopic fracture appearance, side-view fracture path and corrosion-related surface condition of selected Charpy V-notch specimens, as shown in Figs. 8–12. These images provide complementary evidence for interpreting the absorbed impact energy results because they show the visible fracture path morphology, corrosion-product formation and local fracture-surface irregularity. It should also be noted that the fracture surfaces were examined some time after Charpy testing. Therefore, corrosion products observed on the newly exposed fracture surfaces in Figs. 8–12 may have formed after impact testing and should not be interpreted as internal corrosion that existed before fracture. For the uncorroded reference specimens, the side-view images show that the fracture path was generally more uniform and nearly vertical in several specimens tested at higher temperatures. In contrast, a more inclined and locally deviated fracture path was observed in the low-temperature reference condition. This change is consistent with the strong decrease in absorbed impact energy as the test temperature decreased from 23 °C to sub-zero temperatures. The inclined fracture path is consistent with a change in the macroscopic crack trajectory as the absorbed impact energy decreased; however, the stereomicroscope images do not identify the underlying fracture micromechanism.

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