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The authors discuss the mechanism of breaking coal by blasting with a view to optimizing this method of dynamic treatment of coal and improving drilling-and-basting performance. A combination model of high gassy coal is used to describe the connection between coal breaking by blasting and subsequent gas liberation. This model and the smoothed-particle hydrodynamics method are used to study evolution of damage zones and stress–strain behavior of coal in the neighborhood of a blasthole after explosion. The research findings help predict coal response to the dynamic impact.

The preparation mechanism for gas-dynamic fracture of outburst-hazardous coal band during an explosive effect on a coal seam is considered. The conditions for crack formation in the zone farthest from the blasthole are studied, as well as simulation of induced cracks filling with methane, which was initially in coal in a dissolved state, and estimation of the start time for crack development due to the pressure of free methane. It is found that, depending on the mechanical and diffusion parameters of coal, the start time for crack development can vary from tens of seconds to many hours. The study results can be useful in developing a theory of explosive effect on a coal seam in a set of measures to reduce the risk of sudden outbursts of coal and gas.

Underground mining of coal seams often causes problems associated with the imbalance of the natural coal-methane system. In some cases, during anthropogenic action on the coal seam, an extremely large amount of methane is released, which leads to disasters—methane explosions or emissions of coal and gas, in other cases, very little free methane is released, which greatly complicates the commercial production of coal mine methane. Dynamic impact is one of the tools for managing the conditions of coal seams. As a result of explosive action, extended cracks can form in the coal seam for it degassing. The aim of the work is to consider the type of failure to find ways to optimize the explosive impact on the coal seam. This may contribute to the development of a drilling and blasting passport, depending on the objectives of this impact. To this goal, the work uses a joint model of a gas-saturated coal seam to describe the hierarchical relationship between explosive damage to the coal seam and gas evolution [1]. Based on this model, using the numerical simulation by the smoothed particle hydrodynamics method (SPH) [2, 3], the development of the fracture zone is studied and the stress-strain state of the formation near the face before and after the explosion is determined. The obtained patterns help to predict the reaction of coal to a dynamic effect. This is of great importance for the technology of preliminary degassing of coal seams and for the technology of provoking controlled emissions of coal and gas.

The fracture of brittle specimens with an initial crack under uniaxial compression is studied experimentally. The effect of the crack orientation on the fracture of the specimens is examined. It is established that the crack nucleates and advances mainly in the loading direction (longitudinal fracture being predominant). The brittle material is modeled taking into account the difference between the compressive and tensile strengths of the material, the accumulation of damage, and the degradation of strength. The results obtained with the model in analyzing the fracture of brittle specimens with an initial crack under uniaxial compression are in satisfactory agreement with experimental data Introduction. It is very difficult to analytically describe the stability of compressed brittle bodies with an initial crack because of the complexity and diversity of the associated processes. The analytic solutions found in (3-6, 15, 18) are based on some assumptions and in many cases inadequately describe the real fracture behavior of brittle bodies with cracks. The stability of brittle bodies with an initial crack is addressed in many experimental studies (2, 6, 16, 19). Some of them are concerned with the limiting state of a brittle solid under various types of loading, and some with the stability of thin glass or polymethylmethacrylate plates with an initial crack under tension. There are very few experimental studies of the stability of brittle bodies with an initial crack under uniaxial compression. This problem is of importance for studying the fracture of rocks. The reason why the problem has not been studied adequately is the difficulty of fabricating specimens so that they do not buckle under compression. Therefore, the numerical simulation of the fracture of solids and the analysis of the accompanying phenomena were performed in many studies. A considerable advance in this field was made in (11-14, 17, 20). In view of the above, we set out here to develop a procedure for preparing brittle specimens with an initial crack, to experimentally study the fracture of such specimens under uniaxial compression, and to develop a brittle material model that would provide as real as possible (being in best agreement with experimental observations) description of the fracture of loaded

A phenomenological model of dynamic fracture of solids and a two-level fracture criterion, which takes into account increase in the degree of damage of materials on loading, are proposed. Within the framework of a model of elastoplastic solid, solutions of a three-dimensional problem of the dynamic fracture of rock on its interaction with the cutting tool have been obtained by a numerical method. The effect of the criterion on the development of the fracture process and the dependence of cutting force on time are considered.

We study the stress-strain state formed in a plate containing a stationary crack of finite length subjected to pulsed loading, develop a model of quasibrittle fracture caused by loads of this type, and deduce analytic expressions for the stress-strain state near the tip of the stationary crack in the plate. The proposed model admits rigorous physical justification and enables one to describe the development of brittle and quasibrittle fracture processes in materials with cracklike defects under dynamic and static loads within the framework of the same approach. The results of numerical simulation are in good qualitative agreement with the experimentally established regularities of the behavior of the critical parameters of fracture processes.

The dynamic loading of a rock mass during explosion of a borehole explosive is studied using a continuum mechanics approach in two-dimensional plane and axially symmetric formulations with the aid of a modified finite element method [1, 2]. This numerical technique makes it possible to study wave processes in a rock mass owing to explosions of single charges as well as those of systems of borehole explosives under different conditions. These include varying the site at which the charge is initiated and accounting for the propagation velocity of detonations in the explosive, so it is possible to calculate the shape of the stress field created by a charge with a given design. Numerical simulation of the explosion process for multiple borehole explosive charges with delays relative to one another can be used to obtain the optimum delay time for initiation and the distances between the charges. These results can also extend our concepts of the processes taking place in a rock mass during explosive fracture.

A method is developed to describe the formation of the stress‐strain state in the vicinity of the tip of a stationary crack in a three-dimensional plate under dynamic loading. The energy model used to describe the formation of the stress concentration zone around the crack tip is modified to take into account the transient character of the loading process and the influence of the free surfaces of the plate on the stress‐strain state of the central part of the sample. The method is useful for describing static and dynamic brittle fracture from a unified point of view. The formation of a stress wave field in a three-dimensional plate under impulsive loading is significantly influenced by the presence of crack-type flaws and the diffraction of stress waves from the free end surfaces and main faces of the plate, res ulting in the generation of unloading waves. Their multiple interference makes it very difficult to analyze experimental data on the dynamic fracture of flawed plates In this paper an energy model of the formation of a stress concentration zone in the vicinity of the tip of a stationary crack under dynamic loading [1] is used to describe the stress‐strain state of a three-dimensional plate containing a central c rack. Here the model is modified to account for the transient character of the loading process and the influence of the free surfaces of the plate on the stress‐strain state of the central part of the sample. 1. Stress‐Strain State of a Continuous Three-Dimensional Plate. In the initial stage we consider the stress‐strain

A procedure for numerical modeling of the behavior of various planar samples of construction materials containing static and moving cracks under dynamic loading is formulated on the basis of the model of a linearly elastic solid and the application of a continuum mechanics approach. Calculations are carried out by a modified finite element method using a Lagrangian differencing scheme. The results of test calculations are given for comparison with data from a physical experiment. The comparison favorably supports the reliability of the results.

Some results of mathematical modeling of high-velocity collisions of solid deformable bodies are presented. A model is presented of a porous elastoplastic medium whose matrix undergoes a polymorphic phase transition during deformation, and approaches to the calculation of dynamical failure are examined. Finite-difference methods for solving boundary-value problems are briefly reviewed. The interaction of projectiles, having different shape, with different targets (semiinfinite, two-layer, separated) is investigated and the process of spall failure in porous media and media undergoing a polymorphic phase transition is examined on the basis of mathematical modeling.