13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Figure 12. Relationship between Schmid factor for twinning and (a) nominal stress of AE peak and (b) peak of AE energy of each specimen Fig. 13 shows σAEstart of each angle and each annealing condition. σAEstart is defined as the stress at which AE energy is over 0.01 V2. At this point, AE energy is especially higher than noise level, and it is easily said that AE energy is released by certain mechanical behavior other than noise. After annealing, in both 285°C and 450°C, σAEstart is almost the same, and the value is less than 20 MPa. However, before annealing, σAEstart is over 30 MPa and has anisotropy. It can be said that when annealed, nominal stress at which AE energy starts to be released is lower and has weaker anisotropy. Figure 13. Nominal stress of AE start of each specimen Fig. 14(a) plotted the relationship between grain size and σAEp. D is an average grain size, d to the negative one-half power. By annealing, d become larger and D becomes smaller. In each angle, there is linear relationship between D and σAEp. In other words, Hall-Petch equation, which is shown below, is formed in this result; .
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