Issue 52

J. Akbari et alii, Frattura ed Integrità Strutturale, 52 (2020) 269-280; DOI: 10.3221/IGF-ESIS.52.21

As illustrated in Fig. 3, compared to the energy method, wavelet transforms are very sensitive with respect to the starting position of extension and disorders have been appeared in these positions, and this drawback made the damage detection impossible. Additionally, the performance of the first mode shape was better in comparison with the use of higher mode shapes. In other words, when the higher mode shapes have been used for finding the locations of damaged elements, negligible knobs or disorders have been seen. Therefore, by these small disorders, detections were not possible. As depicted in Fig. 4, signal energy could successfully detect the damages near the supports of the pined-pined beams, while the fictitious mode shape extension from the end of the beams is unnecessary.

Figure 4: Damage detection using signal energy for scenario no.3 and no.4. Damages in elements 5 and 95 (a), and Damages in elements 1 and 99 (b). Fig. 5 presents the abilities and sensitivities of the defined methods for different values of the damage intensities. Signal energy could detect damage for various intensities of damaged elements with specified knobs in the graph (a). However, in the wavelet method, all of the intensities are the same which is not a good sign for this method.

Figure 5: Damage detection using signal energy for scenario no.5 (a) and scenario no.6. (b).

Fig. 6 (graphs a,c) shows that the wavelet transforms for clamped-clamped boundary conditions in contrast with pined pined supports, have better performance even for damaged elements with 5% intensity deficiency. Therefore, for such boundary conditions of the beams, the wavelet coefficients are relatively able to detect the local damages. As can be seen from Fig. 6-c, when the damaged elements are close to each other, a significant disturbance appears in the vicinity of the damaged elements. In the clamped-clamped beams, when the damages are near the supports, because of the existence of disorders due to the supports, the wavelet coefficients are not able to detect the damages and extension of the mode shapes could not resolve this deficiency (graph a). Graphs b, d in Fig. 6 reveal that signal energy is successful in detecting damages in clamped-clamped beams. However, it should be noted that mode shapes in this type of beams are not a sinusoidal form, and the energy of mode shapes is not constant but had a curved form. In such a situation, if the damaged

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