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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is recorded using sensors of 3 types. They are 7 strain gauges; 7 one-component piezo-accelerometers and 6 acoustic emission sensors.

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Fig. 1. (a) Experimental sample with the sensors of 3 type; (b) graphs of changes in static load and impulse force.

The loading is carried out stepwise, with increasing the load at each step and reset to zero before the next step. The vibration diagnostic procedure is performed after each loading step when the structure is unloaded. Excitation of vibrations is performed using a striker of 470 grams equipped with an accelerometer. The place of application and the direction of the striker impulse load F s are shown in the figure with an orange arrow. Acoustic emission signals are recorded continuously, excluding impact period. Figure 1b presents a graph of the change in the self-balanced force F s at each loading step and a graph of the change in the impulse force, obtained from the accelerometer on the striker. 3. Experimental results In the experiment, the response of the structure to applied quasi-static load was evaluated. This response was presented as the changes in the deformation field, in the vibration properties of the structure and in the acoustic emission signals. 3.1. Deformation response of the structure to increasing static load Figure 2 shows the change in the strain measured at three points (S1, S3, S4), located at the central crossbars of the 2nd level. The graphs correspond to 6 initial loading steps. Similar data were obtained for all points of the structure equipped with strain gauges. Bottom diagram in Figure 2 shows the change in the strain with distance from the loading zone. The strain values are maximal near the location of the static load and rapidly decrease with distance from it. So, at a distance of 5 meters, the strain is reduced by 30 times. To evaluate the deformation response of various parts of the structure to increasing static load, we propose to calculate the coefficient / ij j ij K F    at each loading step. For the i -th point of the structure, it is equal to the ratio of applied force j F at the j -th loading step to corresponding local strain ij  . This coefficient changes at each loading step, and we can trace how this value varies with increasing load. The diagrams on Figure 3 show changes in the coefficient ij K when the static load increases from 0 to 160 kN. As can be seen from the graphs, the curves behave non-monotonically with increasing load. The graphs related to the