13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- The rate of change of the natural frequencies before and after the injury is shown in Fig. 3, efficient frequency threshold is set as 0.4% ≥ iδ . As Fig. 3 shows, the damage determination efficient modes are mode 1 and mode 4. 3.4. Damage location identification Information function is established using the changes of element strain energy before and after injury, wavelet transform is used to determine the parameters ( DI ) for the location of damage. j DI of efficient modal shown in Fig. 4. By setting the threshold （ 2> DI ）, we can clearly determine that the element 55 to 59 crack damage occurs. This is is very consistent with the actual damage location. Results of location damage identification shown as table 1. Identification error is 3%, it proved that the method of damage location identification has a higher accuracy. 3.5. Identification of injury severity Element damage factor is calculated applying Eq.25, the results of calculation shown as table 1. As shown in Table 1, actual injury and calculation of injury is very close. Identification error is 6.2%, it proved that the method of damage severity identification has a higher accuracy. Figure 3 The rate of change of the natural frequency Figure 4 DI value for each element applying of efficient modal
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