PSI - Issue 28

I. Shardakov et al. / Procedia Structural Integrity 28 (2020) 1407–1415 Author n me / Structural Integrity P o edi 00 (2019) 000–0 0

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Fig. 5. Change in the Fourier spectra amplitude at successive loading steps (sensor V7)

Similar plots were obtained for several points of the structure equipped with accelerometers. They are shown in Figure 6. All curves have noticeable bends near the forces of 80 kN and 120-130 kN. This behavior is recorded both by sensors close to the jack, and by remote ones. We associate these peculiarities with the occurrence of damage at these loads. 3.3. Acoustic emission signals caused by increasing static loading A promising method for detecting the formation of damages under static loading of the structure is acoustic emission (AE) testing. Registration of AE signals continuously throughout the entire loading process allows capturing the moment when the local damages begin to occur in some parts of the structure. The graphs in Figure 7 show the number of AE signals recorded by sensors of different location during the loading process. Each figure shows the curves for low, medium and high intensity signals. The number of signals recorded by different sensors differs significantly. The largest signal flow was recorded by sensor A1 located on the 2nd level of the structure next to the jack. The readings of this sensor are 3 orders of magnitude higher than all other readings. But even sensors A4 and A5 remote from the jack at a distance of 4 m clearly show the presence of low intensity signals at a load of more than 80 kN and signals of medium and high intensity at a load of more than 140 kN. Only sensor 6, located on the 4th level, did not register AE signals. It can be noted that more distant sensors begin to pick up AE signals at higher levels of static load. As in the previous cases, it can be noted that at a certain level of static load, the number of AE signals increases sharply. One of these values is about 80 kN and another is about 130 kN. It can be assumed that the noted values of the static load are associated with the occurrence of primary and secondary structural damage in the vicinity of the jack.