PSI - Issue 14

K Lakshmi et al. / Procedia Structural Integrity 14 (2019) 282–289 Lakshmi and Rama Mohan Rao/ Structural Integrity Procedia 00 (2018) 000–000

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Fig. 3. Damage diagnosis of simply supported Beam-Test case-1: (a) Reconstructed signals of healthy and current data of Sensor-6; (b) Normalised damage index evaluated using distances of ARMAX models in subspace angles.

The minor damage is inflicted at approximately one-third span from both the supports of the beam (i.e. in element no. 5 and element no.12) by applying the static loads in small increments. The minor cracks appear when the static load applied is nearly 12KN as shown in Fig.4. The experiment with dynamic excitation force is performed to create test data (acceleration response) of the beam with minor damage and is referred to as ‘Damage’. The acceleration data of ‘Healthy’ and ‘Damage’ are used as baseline and current data respectively. The cross-correlated signals of the baseline and the current data are fed to the EMD with intermittency and all the IMFs are extracted. The critical IMFs are selected using the correlation coefficient method and are added up to reconstruct the new signal as shown in Fig. 5(a). Subspace angles are evaluated to calculate the distance between ARMAX models of the reconstructed healthy and current signals. The normalized values of subspace angle based damage indices of ARMAX, shown in Fig. 5(b), clearly reflect the spatial location of damage (at one-third of the beam from both the supports.).

Fig. 4. Scenario of Damage

5.0 Conclusions In the paper, a novel hybrid technique to identify the location of the minor damage like minor cracks is presented. As, the minor damage creates feeble changes in the dynamic characteristics of only a few modes of the structure, the damage features present in those modal responses get hidden in the overall response (i.e., the measured dynamic signature). Additionally, measurement noise and environmental variability also play their role in masking the minor damage features in the overall response of the structure. In view of this, in this paper, an attempt has been made to isolate these damage sensitive modal responses and reconstruct a new signal accordingly using improved EMD with intermittency criteria. The damage enriched signals isolated by EMD are further used for damage diagnosis using the ARMAX time series model, employing a damage index, constructed from the distance measure of any two ARMAX