13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- the increase of the number of emitted dislocations at lower applied stress intensity factor rate, however, it also decrease at high stress intensity factor rate conditions. The distributions of dislocations at several applied stress intensity factor rate (A) K&=0.56 MPam1/2/s, (B) K&=56 MPam1/2/s are shown in Figure4. In this figure, we considered that dislocation motion is softened when the exerted effective stress at each dislocation takes below 29 MPa. And the hardening is also considered to occur when the effective stress takes between 29 to 81 MPa. At this hydrogen concentration, both the size of plastic deformation zone and the number of emitted dislocations increase due to the softening effect at lower applied stress intensity factor rate conditions. However the hardening becomes dominant at higher applied stress intensity factor rate. This result indicate that the local hardening near the crack tip can occur even the macroscopic softening conditions, and thus the plastic deformation is supposed to be complex in these conditions. 0.01 0.1 1 10 100 1000 10000 Applied stress intensity factor rate [MPam1/2/s] With hydrogen Hydrogen free (CH=0.49/nm) 10-5 10-4 10-3 10-2 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=0.49/nm) Figure 3. Correlation between the applied stress intensity factor rate and; (a): distance of first emitted dislocation, (b): the number of emitted dislocations Figure 4. Dislocation distribution around a crack tip at the stress intensity factor rate of (A): 0.56 MPam1/2/s, (B): 56 MPam1/2/s (a) (b) (A) (B) (A) (B) (A) (B)
RkJQdWJsaXNoZXIy MjM0NDE=