PSI - Issue 32

Irina A. Bannikova et al. / Procedia Structural Integrity 32 (2021) 10–16 Author name / StructuralIntegrity Procedia 00 (2019) 000 – 000

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When registering fractoluminescence with a photomultiplier on an oscilloscope, at least two pulses were recorded, see Fig. 4. The first impulse (A) was accompanied by a characteristic prolonged crackle with small interruptions, and then, after a fraction of a second, a second impulse (B) was observed with a noticeably larger amplitude and shorter duration. In order to avoid signal clipping on the oscilloscope, in the case of another sample, the photomultiplier gain was set to 10 times less (see Fig. 4, bottom screen, right). In the moment when the second pulse (B) is appeared, the specimen was completely destroyed, and the experiment is stopped.

Fig. 4. Signals from the photomultiplier: A – first impulse – 1st stage of destruction (for No. 1) and B - second impulse – 2nd stage of destruction (for No. 1 and No. 5 samples, pictures right).

The data obtained is in good agreement with the recordings of a high-speed video camera. The Fig. 5 shows frames from a video recording of the fractoluminescence of a sample in the destruction process. In the first three frames, you can see how a "web" of vertical and horizontal cracks forms inside the specimen, which corresponds to the 1st stage of destruction. The last two frames show complete destruction and fragments scattering, which is comparable to the second signal from the photomultiplier and the second stage of destruction. After loading the quartz samples, the obtained fragments were analyzed using the method of weighing and processing photographs by Bannikova and et. al. (2016), Bannikova (2017), Davydova and Uvarov (2013), Davydova and et.al. (2014). The resulting fragments were conventionally divided in shape into three types, see Fig. 6: in the plates form (type 1), in the form of volumetric elongated objects (type 2), and in the form of volumetric objects resembling the octahedral shape (type 3). The fragments were sifted through a sieve system (the characteristic mesh size was from 2.5 to 0.05 mm 2 ) and weighed on an electronic balance (HR-202i, error 0.0001 g). On sieves, where there were too many fragments, only a part was weighed (but not less than 0.01 g) and their number was counted. Then, using the proportion, the approximate number of particles of the entire sieve was calculated. On the lowest sieves, the number of fragments was calculated only after processing the photographs or was estimated based on the characteristic size of the sieve under study and the upper one above it. Knowing the density of quartz and the approximate fragment volume, its mass was calculated. Then, the cumulative fragments mass distributions for each tested sample were built.