Fatigue crack growth (FCG) tests for compact-tension specimens of low-carbon steel were performed under various combinations of hydrogen pressures (0.1–90 MPa), test frequencies (0.001–10 Hz), and test temperatures (room temperature, 363 K, and 423 K). For quantifying the FCG acceleration, the hydrogen trapping and diffusivity of prestrained specimens were determined. Depending on the test conditions, the FCG was accelerated. The hydrogen-assisted FCG acceleration always accompanied localized plastic deformations near the crack tip. The onset of the FCG acceleration was roughly quantified by using a simplified parameter representing the gradient of the hydrogen concentration at the crack tip.
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