PSI - Issue 19

Jean-Gabriel SEZGIN et al. / Procedia Structural Integrity 19 (2019) 249–258 Jean-Gabriel Sezgin et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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3.2. Hydrogen content

The hydrogen content was measured after exposing H-charged specimens to air at ambient temperature for durations from 24 h up to 358 h. The resulting hydrogen contents were nearly constant in the whole duration range. In the case of 100 MPa H-charged specimens, the average content was 16.5 mass ppm ± 1.9 mass ppm (based on 27 measures). In the case of 35 MPa H-charged specimens, the average content was 9.6 mass ppm ± 0.5 mass ppm (based on 3 measures). All the fatigue-life tests were completed within 358 h; therefore, the effect of outgassing from the H charged specimen during the test was concluded to be negligible. The results of fatigue-life tests were provided by Figure 2 for different test frequencies and stress amplitudes. On the S - N diagram, the data related to the non-charged and H-charged specimens were respectively plotted in blue and red. A notable H-induced degradation of the fatigue life was observed in the low-cycle regime, especially at lower test frequencies. Oppositely, a moderate H-induced degradation of the fatigue life was observable in the high-cycle regime. Additionally, no H-induced degradation of the fatigue limit was observed. The fatigue limit is the maximal stress amplitude resulting to non-failed specimens at 1 × 10 7 cycles. In the present case, the fatigue limits of non-charged and H-charged specimens were equal to 110 MPa. Figure 3Figure shows fatigue cracks emanating from the notch root observed in the non-charged and H-charged specimens tested at the stress amplitude corresponding to the fatigue limit ( σ a = 110 MPa). These cracks were not detected in the non-failed specimens tested at stress amplitudes of 105 MPa and 100 MPa. Although we do not have a lot of experimental evidences, these cracks are considered to be non propagating cracks. A series of the experimental results suggest that the fatigue limit of the circumferentially-notched specimen was not degraded by hydrogen. 3.3. Experimental evidence of fatigue-life properties in presence of hydrogen

Figure 2 – S - N diagram for the circumferentially-notched specimens tested under a stress amplitude in the [100 MPa; 400 MPa] range, a stress ratio of -1 and frequencies from 10 -3 Hz up to 10 Hz. Non-charged and H-charged specimens were tested in air at room temperature.

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