PSI - Issue 65

Igor Zh. Bunin et al. / Procedia Structural Integrity 65 (2024) 32–38 Igor Zh. Bunin et al. / Structural Integrity Procedia 00 (2024) 000–000

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3. Results and discussion

3.1. Structural surface defects properties and softening of geomaterials as a result of HPEMP effect

The results from SEM-observations of the sandstone and granite samples surface, under study in the initial (before HPEMP treatment) state, indicated the absence of characteristic pronounced microdefects such as cracks and pores. On the surface of the coal samples, few microcracks with an opening equal to 0.2-0.3  m (microns) were present. When analyzing digital SEM images of the surface of coal samples before and after pulse exposure, we focused on the substructure of microcracking. Using the X-ray microtomography method, we obtained images (slices) of the internal structure of coal samples from the outburst (Berezovsky's mine) and non-outburst (Komsomolskaya mine) coal seams. The main difference is that the first sample had a network of microcracks, while the second sample had no microcracks, that is, the coal from the outburst seam had a much greater degree of initial disturbance than the coal from the non-outburst seam. As a result of exposure to HPEMP, the microcracking occurred mainly in samples from the outburst seam. SEM data showed that at pulsed treatment ( t treat. = 300 s), systems of microcracks formed on the surfaces of the coal samples and propagated along strictly linear (Figure 1а) and tortuous trajectories (Figure 1b). The opening (  ) of individual cracks were 1.5–2.5 μm in size. The formation and propagation of microcracks was affected by inclusions in the coal (Figures 1b,c). Structural modifications after pulse treatment were more typical for the samples taken from the outburst coal seam that are brittle. Using the XCMT-method, the images of internal structure of a coal sample were obtained in three mutually perpendicular directions with individual microcracks, which were formed as a result of electromagnetic pulse treatment ( t treat. = 300 s). A system of extended microcracks up to 5.0–6.0 mm long and with an opening value of up to  = 30–40 µm in size was observed in samples from an outburst coal seam.

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Fig. 1. The microdefects on the coal samples surface after exposure by high-power nanosecond electromagnetic pulses ( t treat. =300 s). SEM; the scales are (a) 5, (b) 10, (c) 5, and (d) 5  m.