PSI - Issue 66

Yamato Abiru et al. / Procedia Structural Integrity 66 (2024) 525–534 Author name / Structural Integrity Procedia 00 (2025) 000–000

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outer surface was reduced by approximately one-tenth in the presence of hydrogen. Fig. 6 illustrates the relationship between aspect ratio, a / c , and crack growth length in the thickness direction, a . The crack propagated in a semi elliptical shape, with the hydrogen-precharged material showing greater growth in the thickness direction. This can be explained as follows: hydrogen tends to diffuse into the atmosphere from the inner and outer surfaces of the metal, reducing its concentration near these surfaces. However, within the metal, hydrogen content remained relatively high, making cracks more susceptible to hydrogen effects in the thickness direction. Kanazaki et al. (2006) conducted fatigue tests on cathodic hydrogen-precharged austenitic stainless steel SUS304, an FCC lattice structure with a low hydrogen diffusion coefficient. Their results showed that hydrogen accelerated crack growth near the surface, where hydrogen concentration was higher, resulting in a longer semi-elliptical major axis in hydrogen-precharged materials. In contrast, our experiment showed the opposite trend. As the crack progressed to a depth of 4.0 mm and reached the outer surface, the aspect ratio converged to approximately a / c = 0.10–0.14. After reaching the outer surface, the crack continued growing in the axial direction, causing the aspect ratio a / c to decrease further, as shown in Fig. 6, with the trend extending downward parallel to the vertical axis.

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

Aspect ratio, a / c

: Uncharged : Hydrogen-precharged

0

1

2

3

4

5

Crack length in the thickness direction, a (mm)

Fig. 5. Relationship between crack length in thickness direction and number of cycles, N .

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

in the thickness direction, a (mm)

Crack length

: Uncharged : Hydrogen-precharged

1000

10000

100000

1000000

Number of cycles, N (cycles)

Fig. 6. Relationship between aspect ratio, a / c , and crack length in thickness direction, a . c is crack length in axial direction.