PSI - Issue 54

Margo Cauwels et al. / Procedia Structural Integrity 54 (2024) 233–240 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 3. Normalized load (F/A 0 ) versus CMOD curves for SENT tests both in uncharged and hydrogen-charged condition

3.2. Side surfaces In Fig. 4, the side views of hydrogen-charged specimens after testing are shown and compared with the side view of the uncharged specimen. The crack growth behavior was clearly very different for the three tested conditions. For the in-situ tested specimen, the growing crack has two points where the crack splits into two, as well as many small branching cracks. Additionally, for this condition many small S-shaped cracks can be seen in the strain fields ahead of the crack tip. Laureys et al. (2015) previously observed a similar phenomenon for notched flat tensile test specimens. These cracks are found in regions coinciding with high stresses induced by the crack tip, which can therefore be expected to contain more hydrogen. For the ex-situ tested specimen, there appears to be some crack branching at the end of the fatigue pre-crack, however afterwards one crack does dominate. There was very limited secondary cracking observed on the surface otherwise. The crack also appears to grow in a zig-zag pattern, which could be resulting from the orientation of the banding, which is perpendicular to the expected crack growth direction, or from hydrogen promoting crack kinking, which was seen in H-charged compact tension (CT) specimens by Elazzizi et al. (2015).

Fig. 4. Side views of (a) air tested specimen near the end of the test (b) ex-situ tested specimen after the test (b) in-situ tested specimen after the test, with detail.