13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- cutting the specimen vertically to the direction of the crack propagation. The elemental components at the inside of the crack were observed with the auger microprobe. Figure 9 shows the auger spectrum at the bridge formation inside of the crack after the application of the electric current. It is observed that the intensity of the spectral line is strong at the electron energy of Fe and Ni, and Fe and Ni are alloyed on the crack surface. 3.2. Evaluation of crack growth behavior The behavior of the crack growth was evaluated quantitatively in order to research the effect of the crack healing. The crack closure was confirmed at the Specimen B in the same way like Specimen A. Figure 10 shows the crack growth rate as a function of the stress intensity factor range, Paris law, with Standard specimens without the application of the electric current. The fatigue test was conducted at σmax = 150 MPa in the Specimen B after the application of the electric current. Figure 11 shows that before and after the application of the electric current in the Specimen B. The solid line indicates the approximate line of the results of Standard specimens without applying the electric current. The open and solid symbols B show the behavior of the crack growth in specimen B before and after the application of the electric current, respectively. It was observed that the crack growth rate decreased from 3.69×10−8 to 2.52×10−8 m/cycle just after the application of current compared to that of Standard specimens. Crack propagation Figure 5. Image of fatigue crack before the application of the electric current and the measurement points of the crack width in Specimen A 5 1 3 4 2 Figure 4. The relationship between atomic concentration of O, Cr, Fe and Ni and depth from the specimen surface after Ni striking 100 80 60 40 20 0 Atomic concentration, y % 2000 1500 1000 500 0 Depth, d nm O Fe Ni Cr O Cr Fe Ni
RkJQdWJsaXNoZXIy MjM0NDE=