PSI - Issue 30

O.V. Startsev et al. / Procedia Structural Integrity 30 (2020) 162–166

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M.P.Lebedev et al / Structural Integrity Procedia 00 (2020) 000–000

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conducted within the 50 kHz-500 kHz frequency range. Signals were recorded with a sampling frequency of 2.5 MHz. The measurements showed that the acoustic emission was within the limits of background noise in all the dried samples and in the water-saturated samples with surface defects upon cooling. The characteristic of dried sample with a 15.7 mm-long crack is given in Fig.1. The acoustic emission parameter U was characterized by single emissions caused by mechanical noise from the movement of dry ice granules after placing the sample into the container. Acoustic emissions of KAST-V samples containing 0.98% water with edge-split layers are different. Fig. 2 shows acoustic emissions of such samples with the impulse amplitude more than twice higher than the background noise. This allows us to link acoustic emission impulses with ice crystallization, an increase of internal stresses at transition of water into ice at the crack tip, and with numerous micro-damages of the binder generating acoustic impulses.

Fig.1. Root-mean-square value of voltage of acoustic emission of the dried sample of KAST-V with a 15.7 mm-long crack.

Fig.2. Root-mean-square value voltage of acoustic emissions of the KAST-V sample with a 15.7mm crack and 0.98% water saturation.