PSI - Issue 42

Christina Margaraita Charalampidou et al. / Procedia Structural Integrity 42 (2022) 1708–1713 Charalampidou et al./ Structural Integrity Procedia 00 (0000) 000 – 000

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3.2 Analysis of the experimental results Fig. 2 shows the typical experimental tensile flow curves of AA2198-T8 specimens exposed for various times to the three investigated corrosive solutions. Essential stress decrease was noticed for the specimens exposed to EXCO solution, Fig. 2a, even after short exposure times (e.g., 6 h). On the contrary, no significant reduction of axial nominal stress is evident for the specimens exposed to more mild solutions, such as 3.5 wt. % NaCl (Fig.2b) and Harrison (Fig. 2c), even after the highest exposure times (e.g., 4320 h). Regarding axial nominal strain, specimens exposed to EXCO solution exhibited a considerable decrease for short exposure times and up to 12 h of exposure, while further corrosion exposure seems not to affect the strain-to-fracture significantly. The same trend was evident for the specimens exposed to Harrison’s solution , but higher degradation of the axial nominal strain was observed especially after 168 h. For the case of NaCl solution, no significant decrease of axial nominal strain was noticed for the short exposure times and up to 720 h, while essential degradation is evident with increasing exposure time. It is worth mentioning that higher ductility degradation was observed at the time range between 720 h to 2160 h and 2160 h to 4320 h for the specimens exposed to NaCl solution, with axial nominal strain being essentially reduced approaching conditions of brittle fracture (orange curve in Fig. 2c), probably due to changes in corrosion mechanism. Decrease in axial nominal stress is attributed to the decrease of effective thickness due to micro-cracks evolution while decrease of axial nominal strain at short exposure times, where pitting corrosion is limited, is due to hydrogen embrittlement according to Alexopoulos et al. (2017).

600

600

Reference

Reference

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6 h

200 Axial nominal stress σ [MPa] 300 400

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100 Nominal axial stress σ [MPa] 200 300

168 h

720 h

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AA2198-T8, t = 3.2 mm L rolling direction Exposure time to EXCO solution

AA2198-T8, t = 3.2 mm L rolling direction Exposure time to 3.5% wt . NaCl solution

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0 2 4 6 8 10 12 14 16 18 20 0

Nominal axial strain ε [%]

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(b)

Axial nominal strain ε [%]

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720 h

168 h

2160 h

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0 2 4 6 8 10 12 14 16 18 20 0 AA2198-T8, t = 3.2 mm L rolling direction Exposure time to Harrison's solution (diluted version)

(c) Fig. 2: Typical experimental tensile curves of pre-corroded specimens of AA2198-T8 exposed to (a) EXCO (b) 3.5 wt . % NaCl and (c) Harrison’s solution. Axial nominal strain ε [%]