13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- 3. Experimental results 3.1. Observation of fatigue crack The elemental components were observed with an auger microprobe to confirm the effect of the surface-activated pre-coating technique. Figure 4 shows the relationship between atomic concentration of O, Cr, Fe and Ni and depth from the specimen surface after Ni striking. The Fe and Cr are the main element of the specimens, SUS316, and Ni is the element coated by the surface-activated pre-coating technique. It is observed that the oxide layer, O is almost eliminated at the surface of the specimen and Ni coating film is approximately 630 nm thick. The crack state on the specimen surface was observed with SEM. Figure 5 shows the fatigue crack shape before the application of the electric current in Specimen A. The points to measure the change of the crack width were indicated. Figure 6 shows the change of the fatigue crack shape at each application of the electric current in Specimen A. It is observed that the crack was closed for almost every application of the electrical current. Figure 7 is an enlarged picture at the area near the point 3 which is approximately 900 m away from the crack tip before the application and after the 12th application of the electric current in Specimen A. The adhesion between the crack surfaces was observed and it is observed that the application of electric current also has an effect on the area far from the crack tip. Figure 8 shows the change of crack width for every application of the electric current. Compared to before the application and after the twelfth application of the electric current, the crack width near the notch decreased from approximately 39 m to 8.5 μm. After the twelfth application of the electric current, the whole crack was closed 75-97 % from original crack, and the whole crack width was less than 10 m. The bonding of the crack surfaces was confirmed by Figure 2. Schematic diagram of surface-activated pre-coating technique: (a) Electrolytic cleaning, (b) HCl activating, (c) Ni striking (a) (b) (c) Figure 3. Applying electric current Electrode Specimen Fixture
RkJQdWJsaXNoZXIy MjM0NDE=