PSI - Issue 77

Jan Kec et al. / Procedia Structural Integrity 77 (2026) 264–271

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3. Results and discussion Figure 3 presents the FCGR as a function of ΔK for eight tested samples. Hydrogen-charged samples (red symbols/lines) exhibited significantly higher FCGR compared to air-tested specimens (blue symbols/lines). The ASME B31.12 upper-bound curve is included for reference (black line), while the legend displays the experimentally derived Paris law constants. The hydrogen- enhanced crack growth was most pronounced at low ΔK values (initial test phase), with the effect progressively decreasing at higher ΔK levels. This attenuation may result from either: (1) electrolyte depletion reducing hydrogen generation efficiency, or (2) crack propagation into regions not fully saturated with hydrogen. The electrolyte depletion hypothesis is more plausible, as similar behavior has been reported earlier (Alvaro et al., 2019). Fractographic analysis at ΔK = 20 MPa .m 0.5 (Fig. 4) revealed distinct fracture mechanisms. Air-tested samples displayed characteristic ductile striations (Fig. 4a), i.e. crack propagation per cycle. On the other hand, the hydrogen charged sample shows a mixed type of fracture, where quasi-cleavage facets with ridges and indistinct striation patterns occur.

Fig. 3. FCGR data for samples tested in air (blue symbols and lines) and hydrogen charged (red symbols and lines).

(a)

(b)

Fig. 4. F racture surfaces at ΔK = 20 MPa.m 0.5 of the sample tested in air (a) and hydrogen charged (b).