Issue 78

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

Figure 13: SEM images of selected near-fracture cross-sections located approximately 10 mm from the fracture surface: a–b) uncorroded reference specimens tested at 23 °C, c–d) 30-day seawater specimens notched after corrosion exposure and tested at 0 °C, e–f) 30-day seawater specimens notched after corrosion exposure and tested at 23 °C, g–h) pre-notched 30-day seawater specimens tested at 0 °C. The images show ferrite–pearlite microstructure, local heterogeneity and discontinuity-like features. The specimens exposed to seawater for 30 days, notched after corrosion exposure and tested at 23 °C are shown in Fig. 13(e, f). The specimen with 12.82 J in Fig. 13(e) shows several dark discontinuity-like features and a locally heterogeneous ferrite–pearlite distribution. By comparison, the specimen with 31.34 J in Fig. 13(f) exhibits a more continuous ferrite– pearlite structure, with less pronounced isolated defects at the observed location. Although the average absorbed energy of this group was lower than that of the uncorroded 23 °C reference group, the selected cross-sections show different local ferrite–pearlite distributions and discontinuity-like features at the examined locations. However, these observations do not demonstrate that the microstructural differences in the selected fields controlled the measured absorbed impact energy. The pre-notched specimens exposed to seawater for 30 days and tested at 0 °C are shown in Fig. 13(g, h). The lower-energy specimen in Fig. 13(g), which absorbed only 5.80 J, contains a large dark pull-out-like or inclusion-like discontinuity together with additional smaller discontinuities. In contrast, the higher-energy specimen in Fig. 13(h), which absorbed 26.13 J, also shows ferrite–pearlite heterogeneity and isolated dark features, but the observed discontinuities are less severe than the large defect-like region seen in Fig. 13(g). Because these features were observed on cross-sections away from the actual fracture surfaces, they cannot be linked directly to crack initiation or crack propagation. Furthermore, without EDS analysis, the dark features cannot be definitively identified. The comparison therefore highlights local variability between the selected fields but does not provide a micromechanism explanation for the notch-timing response. Overall, SEM of the selected near-fracture cross-sections showed a ferrite–pearlite microstructure with local variations in pearlite distribution, grain-boundary contrast and discontinuity-like features, including void-like, pull-out-like and inclusion like regions. Since no EDS analysis was performed, these dark features cannot be definitively identified as inclusions; therefore, they are described using the suffix “-like”. Within the selected paired observations, some lower-energy specimens displayed more pronounced local heterogeneity or larger discontinuity-like features than the corresponding higher-energy specimens. However, only selected cross-sectional fields were examined, and these fields were located approximately 10 mm away from the actual fracture surfaces. This qualitative pattern should be considered exploratory and does not establish a general or causal relationship between the observed microstructural features and absorbed impact energy. Because the SEM observations were obtained from near-fracture cross-sections rather than from the actual fracture surfaces, they were

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