PSI - Issue 28

I. Shardakov et al. / Procedia Structural Integrity 28 (2020) 1407–1415 Author name / Structural Integrity Procedia 00 (2019) 000–000

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3.2. Vibration response of the structure to increasing static load Another method of recording changes in the deformation state of the structure is vibration diagnostics. It allows you to detect changes in the vibration properties of the structure, which are caused by the appearance of damages. The vibration diagnostics procedure was carried out according to the following algorithm. After each loading step, structural vibrations were excited by the striker, and the set of acceleration vibrograms was obtained and then compared with the vibrograms recorded prior to loading. Figure 4 shows the vibrograms obtained for the accelerometer V7 located on the column near the jack. The vibrograms are normalized to the acceleration amplitude of the striker. The vibrograms of the first two loading steps (left column) are almost identical. But the vibrogram obtained at the 37th step (when the static load is 160 kN) significantly differs from the initial one (right column). Figure. 4 gives the vibrograms at an interval of 250 seconds after the diagnostic impulse and in details at the initial stage of the vibration process.

Fig. 4. Comparison of vibrograms obtained at various loading steps (sensor V7)

The comparison of vibrograms obtained at different loading steps can be efficiently performed using Fourier analysis. In Figure 5, on one graph, the Fourier images of vibrograms obtained at 37 successive loading steps are superimposed. It can be seen from the top figure that there are 2 frequencies at which the divergence of the graphs is maximum. These are the frequencies of 0.36 kHz and 1.62 kHz. Having fixed one of these values, it is possible to trace how the Fourier spectrum amplitude changes after each loading step. The graphs obtained for each of the marked frequencies are presented at the bottom of the figure. It is interesting to note that both diagrams show a sharp change in trend when the force is about 80N.