New results are presented from experimental studies of the nonthermal effect high-power (high-voltage) nanosecond electromagnetic pulses have on the development of microdefects in rock samples. Scanning electron microscopy is used to assess microstructural modifications in samples, along with X-ray microtomography for coal. Sizes of the gaps in microcracks are measured, their structural features are analyzed, and a possible mechanism of miсrodefect formation is discussed.

Explosive dynamic impact on coal samples placed in steel storage ampoules is investigated experimentally. The structural features of coal and the nature of its fragmentation are studied via electron microscopy and laser spectrometry for particle size. The different reaction of coal to the impact was determined, depending on the content of gas (methane) in them and their predisposition to dynamic gas destruction. A high share of particles with sizes of around 0.1 microns is observed in disintegrated samples of coal containing methane and prone to dynamic gas destruction, while particles with sizes on the order of several microns formed a substantial fraction of other coal samples. The main phenomenological difference was that storage ampoules with gas-containing coal were partially destroyed during the tests. The possibility of using the results from coal tests to predict hazardous dynamic gas phenomena in mines is considered.

РоссияОбсуждены возможности и результаты применения методов рентгеновской компьютерной микротомографии, ультразвуковых измерений, нано-и микроиндентирования, контроля образования субмикронных частиц применительно к изучению процесса динамического разрушения горных пород.Для изучения распределения пор и микротрещин в объеме образцов использован метод рентгеновской компьютерной микротомографии, для контроля состояния образцов до и после динамического воздействия -ультразвуковой метод.Методом микро-и наноиндентирования выполнено

The researchers study the effect of water on the strength of small-size specimens made of metamorphic rocks (carbonaceous quartzite, serpentine) and an analog of sedimentary rocks (sand-and-cement mixture, or artificial sandstone) exposed to diametral compression. It is found that the specimens exhibit the same brittle deformation behavior after water storage for a day. All specimens show reduced strength while quartzite and serpentine feature a decrease in deformability down to failure. Microscopic fracturing is viscoelastic and independent of water. It is suggested that the influence of water on the deformation behavior of the specimens can be explained by the Rebinder effect.

Size effects in the hardness of individual phases and inclusions of multiphase materials are studied via micro- and nanoindentation for a number of rock samples (polycrystalline ferruginous quartzites, granite, anthracite, sandstone, marble, and verd antique). The distribution of the local physical and mechanical properties of the studied materials is charted. Size effects in hardness and correlations between the distribution of local physical and mechanical properties and the morphology of the studied samples are found.

The microstructural characteristics of granite are studied experimentally by means of electron microscopy and X-ray microtomography. Images are obtained of the pores and microcracks on the surfaces and throughout the volumes of granite samples, allowing estimates of the sizes and distribution of microdefects inside them. The advantage of using experimental data in analyzing the structural characteristics of different materials is noted.

Size effects in the local mechanical properties of multiphase materials are studied by means of micro- and nanoindentation. The numerical values of the elasticity modulus, hardness, and crack resistance of single phases and interphase boundaries in several rock samples (polycrystalline banded iron formations, granite, anthracite, sandstone, marble, and serpentine marble) are determined. The strongest and weakest intergrowth boundaries in the investigated materials are established. Thermal activation analysis is performed, and the activation and energy characteristics of local deformation in a material under an indenter are identified. The predominant micromechanisms of plasticity in single phases and inclusions in rocks under the action of high local stresses are identified.

Aspects of the scale effect in rocks are considered within the statistical theory of strength. The results from testing the strength of rock samples of different sizes are presented. It is shown that the average tensile strength falls slightly, and its values drop substantially when the sizes of samples increase. A procedure is developed and tests are performed with the compression of granite samples ~6 mm in diameter. The possibility of using this procedure to identify the strength properties of rocks with allowance for the scale effect is discussed.

The formation of cracks in a natural material (granite) resulting from an explosive action is examined. Images of crack fragments and relief are obtained at different degrees of magnification using optical, electron, and confocal laser scanning microscopy. The parameters of cracks as 3D objects are determined with allowance for the distance from the impact source. The roughness of the crack edges and the local increase in their width at a certain stage of propagation indicate a jump-wise character of their development, due possibly to aspects of the zone of failure localization forming at the tip of the crack in granite as a polycrystalline material.