generate macro cracking which results in stress relief and therefore decrease of the AE amplitude. Then the micro cracking would rebuild up again so that stepwise AE amplitude is observed. Obviously, the micro cracking or stress concentration build up didn’t show regular trend, occasionally, sometimes it builds up quickly, sometimes it takes a long resting time before micro cracking is rebuild up again. Figure 4. AE hit rate and amplitude at location C from 139.9 elapsed fatigue hours Crack initiation at 142.3 fatigue hours Significant AE activity lasted for 4 hours (a) AE hit rate (b) AE amplitude in the zoomed area (c) AE amplitude in a minute The time interval between two AE hits corresponds to one fatigue cycle Figure 5. AE hit amplitude versus testing time that shows stepwise crack growth. (a) AE amplitude (b) AE amplitude in the zoomed area
RkJQdWJsaXNoZXIy MjM0NDE=