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

2

33

Nomenclature HPEMP high-power nanosecond electromagnetic pulses E electric field strength, V×m 1 t treat. treatment time by high-power nanosecond pulses, s HV Vickers microhardness, kgf/mm 2 HV relative variations in microhardness, % SEM scanning electron microscopy XCMT X-ray computer microtomography  crack opening (displacement),  m

1. Introduction

At present, in the developed countries of the world, 5–8% of all electricity produced is spent on mechanical methods of mineral processing, and the energy consumption for grinding (mechanical comminution) approximately consist of 80% from this part generated electricity. Non-mechanical Pulsed-Power technologies (such as mechanochemical, radiation, ultrasonic, electrochemical, plasma impacts, and electro-physical pulsed technologies using high-voltage pulse discharges) are actively developed and used to achieve the most complete opening of finely disseminated mineral complexes of ferrous, non-ferrous, precious and rare metals and selective disclosure of mineral splice. Such methods appear to be highly promising, contributing to the selective disintegration of minerals along interfacial boundaries through the formation of microcracks and electric breakdown channels without excessive over-grinding, and thus they saving energy consumption, see, e.g., Chanturiya et al. (2001, 2011); Kurets et al. (2002); Chanturiya and Bunin (2007); Chanturiya (2017); Bunin et al. (2017); Huang and Chen (2021). Studying the features of crack development is an important problem that attracts great attention in fracture mechanics, physics of materials strength, and geomechanics. The structure of geomaterials contains genetic microdefects, or form as a result of external actions. A change in the shape and trajectory of cracks in brittle materials (geomaterials) during their propagation is one of the important factors revealed by experiments. Much emphasis has been put on problems of the formation and propagation of microcracks in minerals and rocks as a result of mechanical, physicochemical, electrochemical, thermal, electric pulse, and other energy impacts. The studying of the coal (and sandstone) destruction under dynamic impacts is a ground for improving the methodology for predicting catastrophic events in mines in the form of hazard dynamic gas phenomena (the sudden outburst of the coal, rock, and gas), see, e.g., Panchenko (2009). In previous work, see Victorov et al. (2019), the explosive dynamic impact on the structural features of coal samples from explosive or nonexplosive coal seams and the nature of samples fragmentation, preliminarily placed in special storage ampoules was investigated experimentally. Using SEM and laser spectrometry methods, the different reaction of coal to the explosive dynamic impact determined, depending on their predisposition to dynamic gas (methane) destruction. A high proportion of forming particles with sizes of around 0.1 microns is observed in dynamic gas disintegrated methane-containing samples of coal, while particles with sizes on the order of several microns formed a substantial fragmentation fraction of other (low-methane bearing) coal samples. The main way to increase the permeability of coal seams, it can produce the fracture network through using some technical methods in order to promote the gas desorption and flow in the coal. In recent years, a technology of high voltage electrical pulses (HVEP) to improve the permeability of coal seams technology has been developed. The basic principle of this technology is to use electro-hydraulic effect of high-voltage, which can produce shock waves to make coal seam crack, then, the coal seam’s permeability will be enhanced. In paper, see, Chuanjie Zhu et al (2017), it was shown that, anthracite coal porosity (micropore, mesopore and macropore) all increased after HVEP breakdown, and in the process of the electric breakdown, the transient high temperature generated the tensile stresses which urged the coal to produce "exogenetic" microcracks, fractures and intergranular pores. According to the authors, this destruction effect could enhance gas seepage and migration in coal seams.