PSI - Issue 64

Rui-Xin Jia et al. / Procedia Structural Integrity 64 (2024) 799–806 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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(a) 60mm

(b) 75mm

(c) 110mm

(d) 160mm

Fig. 9 Plot of amplitude variation with thickness

5.2. Frequency analysis

In order to investigate the effect of different thicknesses of the outer shell on the frequency of the received signals, the FFT of the received time-domain plots was performed respectively. Fig. 10 shows the frequency-domain plots of the received signals with different thicknesses of the outer shell under a 100 kHz excitation signal. From Fig.10, it can be obtained that the frequency domain peaks corresponding to different thicknesses of the outer shell are about 100 kHz, and the frequency domain peaks corresponding to the specimens with outer shell thicknesses of 60 mm, 75 mm, 110 mm and 160 mm are 0.3748, 0.2943, 0.1736 and 0.1045, respectively. It can be obtained that different thicknesses have a certain effect on the frequency domain peak of the received signal, and the frequency domain peak decreases with the increase of the thickness of the outer shell, as shown in Fig. 11.

(a) 60mm

(b) 75mm

(c) 110mm

(d) 160mm

Fig. 10 Spectrograms at different thicknesses

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

Peak frequency

60mm 75mm 110mm 160mm

Thickness

Fig. 11 Plot of peak frequency versus thickness

5.3. Propagation energy analysis The test results of 60mm and 75mm thickness at 100kHz excitation are analysed by time-frequency transformation and the results are shown in Fig.12. It can be obtained that the energy of the guided wave decreases gradually with the increase of tension at the same outer shell thickness. The main reason is that the outsourced mortar and the rebar under tension, so that the contact friction gradually becomes larger, the contact surface is more compact, and the guided wave is easy to leak into the mortar layer. At the same time, as the thickness of the outer

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