PSI - Issue 54

Robin Depraetere et al. / Procedia Structural Integrity 54 (2024) 172–179 R. Depraetere et al. / Structural Integrity Procedia 00 (2023) 000–000

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(a) L-S plane

(b) L-T plane

Fig. 4: Reconstructed volumes of fractured uncharged (top) and hydrogen charged (bottom) specimens, in the (a) L-S plane and (b) L-T plane.

3.2. X-ray micro-CT: microscopic observations

Figure 4 shows the reconstructed volumes of the uncharged and hydrogen charged specimens that were investigated using X-ray micro-CT. While both halves of each specimen were scanned, only one half is presented for illustrative purposes. Each individual void is colored based on its equivalent void diameter D eq . Voids are significantly present in both the uncharged and the hydrogen charged specimens, and are visibly elongated in the L and the T directions. The development of voids is promoted by a higher stress triaxiality, as they are clearly more present for the specimens with a sharper notch. Despite the observed embrittlement (see Figure 3a), there is no apparent visual di ff erence between the void distri bution of the uncharged and the hydrogen charged specimens.

3.3. X-ray micro-CT: damage quantification

For each scanned specimen, all detected voids are binned into groups of similar equivalent diameter D eq , after which the aspect ratios Δ L / Δ S and Δ T / Δ S are averaged. As rationalized in Depraetere et al. (2023), D eq can be considered to represent the degree of the development of a certain void, starting with the first visible stage after void nucleation ( D eq small). The aspect ratios versus D eq are visualized in Figure 5. The elongation of the voids in the L and T direction with respect to the S direction is seen by the aspect ratios being generally larger than 1 for each condition and geometry. The aspect ratios significantly increase upon void development, suggesting a microscopically anisotropic void growth despite the observed macroscopically isotropic plastic behavior (see Figure 3b). The aspect ratios of the uncharged and hydrogen charged specimens are clearly similar, expect for the specimens with geometry R ∞ where the presence of hydrogen appears to enhance void growth in the S direction compared to the L and T direction.