PSI - Issue 57

A. Radi et al. / Procedia Structural Integrity 57 (2024) 642–648 Achraf radi/ Structural Integrity Procedia 00 (2019) 000 – 000

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hydrogen is in the same order (60 MPa). On the contrary, we observed an opposite effect of hydrogen on the back stress component (X) for both states, the hardening of (X) being about 5% in presence of hydrogen for both states.

No H

H

No H

H

N(cycles )

Figure 1: Stress amplitude () evolution of both metallurgical states HT0 and HT4 hydrogen-charged and free in function of the number of cycles (N); 2 = 0,3%, R ε =-1.

Table 1: Stress values for the first (N=1) and saturation (N=sat) cycles of both metallurgical state's HT0 and HT4 hydrogen-free and charged. Saturation cycle for HT0 is N=100 and N=80 for HT4.

First fatigue cycle N = 1

Metallurgical states. HT0 Hydrogen-free HT0 Hydrogen-charged HT4 Hydrogen-free HT4 Hydrogen-charged

σ a (MPa)

σ eff (MPa)

X (MPa)

418 370 745 700 546 542 780 735

240 180 466 406 258 221 472 374

171 181 274 287 287 318 310 358

Saturation cycle N = sat

HT0 Hydrogen-free

HT0 Hydrogen-charged HT4 Hydrogen-free HT4 Hydrogen-charged

3.2. Slip localization These findings stemming from macroscopic-scale mechanical tests were interpreted through investigations of the microstructure conducted at a finer scale, thereby corroborating our initial analysis. We utilized TEM to compare the dislocation structures of the two metallurgical states with and without hydrogen content. We also used SEM and AFM to measure parameters such as inter-band spacing (I B ) and band thickness (w) for both hydrogen-free and charged samples. Initially, the assessment of strain localization was undertaken by quantifying the inter-band spacing (I B ) and band thickness (w) using Atomic Force microscopy (AFM) and Scanning Electron microscope (SEM). These measurements