PSI - Issue 77

A. Hell et al. / Procedia Structural Integrity 77 (2026) 41–48 Author name / Structural Integrity Procedia 00 (2026) 000–000

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Table 1. J 0.2 -evaluation

Specimen condition

Mean J 0.2 ( kJ/m

2 )

uncharged

1424.4 1273.5

96 hours hydrogen charged

3.4. Characterization of cracks and fracture surfaces A reduction of crack growth resistance can be further derived from optical microscopy images from samples used in J- ∆a -curve measurement. In the hydrogen-charged sample seen in Fig. 4b the ductile crack extends to a length of 5.85 mm from the former fatigue crack tip compared to a ∆ a max of 4.25 mm in the uncharged state (Fig. 4a). At a distance of 1 mm from the crack tip, the opening angle of the cracks has been measured to 29.56° (uncharged) and 25.53° (H-charged) respectively. The results are summarized in Table 2.

Table 2. Maximum crack extension and opening angle of ductile crack fronts measured in optical microscopy Specimen condition ∆ a max ( mm ) Opening angle (°) uncharged 4.25 29.56 Hydrogen charged 5.85 25.53

Fig. 4. (a) Optical Microscopy of center section ductile crack fronts in (a) uncharged and (b) H-charged CT50 samples

Fig. 5. SEM fractography with x500 magnification of the fatigue precracks at 4 mm length. (a) uncharged, 10 Hz;(b) uncharged, 5 Hz.