A. N. Kochanov

Micro- and nano-indentation approach to strength and deformation characteristics of minerals

In focus are methodology and effect of micro- and nano-indentation method in studying local deformation and failure of rocks. By micro- and nano-indentation, numerical values of Young’s modulus, and hardness of rocks and minerals have been obtained. The values of fracture toughness are obtained for separate minerals and at grain boundary. The authors highlight the use perspectiveness of the described method in estimating strength and deformation characteristics of rocks.

Physico-mechanical properties and micromechanisms of local deformation in thin near-surface layers of complex multiphase materials

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.

Emission of submicron particles upon rock deformation

Microparticle emission upon rock deformation is established experimentally. The results from experiments on the uniaxial compression of samples with a through hole as a stress concentrator with the simultaneous recording of emissions of mineral particles using laser spectrometry are presented. Quantitative estimates of the emission of particles in the size range of 0.3–5.0 μm with respect to the acting stresses are obtained.

Wave prefracturing of solid rocks under blasting

Considering features of wave prefracturing (microfailure) of rocks under blasting, the authors put forward a new investigation approach with the use of relations of dynamic elastic stress distribution in rocks and theory of cracks. The obtained relation to estimate prefracturing zone size in relatively solid rocks under confined explosion involves pressure of gases in explosion chamber, rock pressure, crack resistance of rocks, characteristic dimension of natural jointing (presence of defects) and deformation characteristics of rocks. It is shown that dimension of prefracturing zone in rocks depends both on natural and production factors and can differ by a few times.

Formation of microcracks upon the dynamic fracturing of rocks

The results from experimental studies on the parameters of microcracks formed after the dynamic fracture of rocks, performed by means of electron microscopy, are presented. Some physical aspects and mechanisms of the formation of microcracks in rocks are discussed. It is noted that an important characteristic of microcracks is the magnitude of their opening. According to experiments, the minimum value of the opening of microcracks is ~0.1 μm.

Disintegration of rock samples at high pulse pressures

A procedure for and the results from experimental studies of the microstuctural changes in rock samples under the action of high pulse pressure during the passage of shock waves are presented. Images of fragments of the sample surfaces at different scales before and after the action are obtained by electron microscopy. The distribution of microparticles in the size range of 0.3−10 μm, formed as a result of explosive disintegration, is established.

Experimental Study of the Microstructural Characteristics of the Surfaces and Volumes of Granite Samples

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 and Charting the Physical and Mechanical Properties of Individual Phases and Interphases in Polycrystalline Materials

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.

Investigating cracks in natural materials using the example of granite under explosive action

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.

Influence of the scale effect in testing the strength of rock samples

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.