Abstract
In order to investigate the effect of test frequency on hydrogen-enhanced fatigue crack growth in ductile cast iron, fatigue crack growth (FCG) tests were conducted at test frequencies ranged from 0.001 to 5 Hz for the following three cases: Case A; FCG test in air, Case B; FCG test in 0.7 MPa hydrogen gas, and Case C; FCG test in air using specimen charged with hydrogen. In Case A, the FCG rate was nearly constant regardless of test frequency. On the other hand, in Case B, the FCG was accelerated by hydrogen gas (external hydrogen). The crack acceleration in hydrogen gas was peaked out at the frequency of ≈ 0.1 Hz, and in the lower frequency regime the growth rate approached to that in Case A. Moreover, also in Case C, the crack acceleration showed similar frequency dependence, in which the maximum acceleration was occurred at = 0.01 Hz. The difference in the frequency for the maximum acceleration between Case B and Case C is discussed based on the difference in the concentration of hydrogen near crack tip.
