13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- 4.2. High Hydrogen Concentration (CH = 1.24 /nm) The correlation between applied stress intensity factor rate and the distance of leading dislocation from a crack tip (i.e. the size of the plastic zone) at the specific stress intensity factor (K = 0.589 MPam1/2) at high hydrogen concentration is shown in Figure 5(a). The size of plastic zone at this hydrogen concentration becomes typically small. The correlation between applied stress intensity factor rate and the number of emitted dislocation is shown in Figure 5(b). Although, the dislocation emission is enhanced at this hydrogen concentration, the number of emitted dislocations typically decreases. The dislocation distributions are also shown in Figure 6. These results indicate that only hardening can occur at this high hydrogen concentration conditions. 0.01 0.1 1 10 100 1000 10000 Applied stress intensity factor rate [MPam1/2/s] With hydrogen Hydrogen free (CH=1.24/nm) 10-6 10-5 10-4 10-3 10-2 1 10 100 1000 0.01 0.1 1 10 100 1000 10000 Applied stress intensity factor rate [MPam1/2/s] With hydrogen Hydrogen free (CH=1.24/nm) Figure 5. Correlation between the applied stress intensity factor rate and; (a): distance of first emitted dislocation, (b): the number of emitted dislocations Figure 6. Dislocation distribution around a crack tip at the stress intensity factor rate of (A): 0.56 MPam1/2/s, (B): 56 MPam1/2/s 4.3. Hydrogen Effects on Fracture Mechanisms Dislocation slip behavior around a crack tip is enhanced at low hydrogen concentration and low stress intensity factor rate conditions, which result in softening. At the high hydrogen concentration (a) (b) (A) (B) (A) (B) (A) (B)
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