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Tests of model solid propellants based on aluminum dodecaboride AlB₁₂ revealed significant discrepancies between the experimental values of the exhaust coefficient and the temperature of the primary combustion products in the model gas generator chamber compared to their values calculated from thermodynamic equilibrium conditions. A computational and experimental method for determining the thermodynamic characteristics of the primary combustion products for model boron-containing propellants characterized by a low content of oxidizing elements (α < 0.2) is proposed. The method involves experimentally determining the combustion product temperature and exhaust coefficient, followed by calculating the gas constant and adiabatic index of the combustion products. The ranges of possible values of the thermodynamic characteristics and their pressure dependences are determined.

The ignition of pine sawdust (d < 200 μm) and mixed compositions of brown coal particles (d < 3 mm) and pine sawdust in a fluidized bed was studied using localized radiation from a continuous-wave semiconductor laser (λ = 450 nm) with a power of ≤23 W with an exposure time sufficient for ignition and flame propagation over the fuel surface until self-sustaining combustion was established. The dependences of the time to establish self-sustaining combustion and the mass of sawdust burnt out in 60 s at a fixed radiation power on the air flow rate through the fluidized bed were determined, as well as the dependence of the time to establish self-sustaining combustion of sawdust on the radiation power at a fixed air flow rate and the dependence of the time to establish self-sustaining combustion of a sawdust and coal mixture on the mass content of coal in the mixture of 30 ÷ 80% at a fixed radiation power of 23 W. Optimal conditions for establishing self-sustaining combustion of solid fuel in a fluidized bed under laser radiation exposure were determined.

Stage separation is a critical event in multi-stage aerospace vehicles, demanding precise, reliable, and debris-free performance. Flexible Linear Shaped Charges (FLSC) have emerged as an effective solution due to their high cutting efficiency, low weight, and ability to conform to structural interfaces. This study presents a comprehensive numerical and experimental investigation into an FLSC-based separation mechanism, with a focus on optimizing cut quality, minimizing debris, and validating simulation results through testing. Three distinct configurations were modelled using hydrocode software: a baseline flat plate setup (Case A) with an 8.4 g/m FLSC, a modified geometry with an R8 notch to guide fracture (Case B), and a reduced-charge configuration with 4.2 g/m FLSC for shock minimization and single plane cutting (Case C). The simulations employed coupled Eulerian-Lagrangian solvers, advanced material models, and embedded gauge points to capture detonation physics, jet formation, and structural response over microsecond timescales. Case B demonstrated significant improvement in debris reduction, while Case C achieved a clean single-plane cut with no debris. The final configuration was realized and tested experimentally using a flat plate test article. The results closely matched simulation predictions, showing precise separation, intact fasteners, and no flying fragments, thus confirming the effectiveness of the hydrocode-optimized design. This work highlights the potential of hydrocode simulations to guide cost-effective, time-efficient, and experimentally validated design of FLSC-based stage separation systems. The insights gained offer practical pathways for the development of next-generation separation mechanisms in space and missile applications, where precision and safety are paramount.

The generalized stress deviator is introduced as a difference between a stress tensor and a unit tensor multiplied by an average normal stress non-reducible to an octahedral normal stress in a general case. From the condition that the average normal stress of the generalized deviator should be identically equal to zero, a functional equation relative to the average normal stress is obtained. The solution of the equation is given; it depends on one of the functions of two variables. The class of the limiting state criteria formulated relative to the average normal stress and the second invariant of the generalized stress deviator is discussed. It is shown that the von Mises-Schleicher and Mohr-Coulomb criteria belong in this class. Some intermediate cases are also discussed.

The article describes the lab-scale tests of permeability of long-flame coal from the Mokhovsky Coal Mine in Kuzbass depending on the intensity of cyclic treatment of coal with liquid nitrogen. The freezing effect on jointing was assessed by a change in the gas flow and in the ultrasound velocity. It is found that permeability of the test coal in compression rises up to commercially significant values. To reach this effect, it is sufficient to implement three-four cycles of treatment with liquid nitrogen. The treatment decreases the ultrasonic P-wave velocity by up to 6%, which points at the increase in the volumetric density of microcracks.

The accomplished review of the geological and geomechanical conditions at the Tashtagol and Sheregesh deposits shows that the operating mine fields contain small- and medium-amplitude fractures, faults, dikes and ore-rock interfaces. It is revealed that during heading and stoping, geodynamic phenomena arise mostly in the neighborhood of these planes of weakness. The mathematical modeling was used for the stress-strain analysis of rock mass at different slope angles of faults approached by the development headings. It is found that in case of a fault 1 to 3 m wide, the shear of the fault edges along the fault plane at the fault slope angle of 65° can happen when an approaching roadway is at a distance not less than 10 m, at the slope angle of 45°-at a distance not less than 20 m and at the slope angle of 15°-at a distance not less than 40 m. For the faults 5 to 10 m wide, at the fault slope angle of 65°, no shearing takes place, at the slope angle of 45°, shearing can happen when a roadway approaches the fault at a distance not less than 5 m and at the slope angle of 15°-not less than 30 m.

The authors revealed the dependence of the dehydrating activation energy parameters in rocks on the phase ratio of β-quartz to α-quartz. In rocks with the predomination of β-quartz (β-quartz / α-quartz > 1), rockfalls are observed and the ratio of the dehydrating activation energies of crystallization water (chemically bound) and adsorbed water (physically bound) is less than 1. This is reflective of the build-up of free and physically bound water which penetrates defects in rocks due to the phase transition of quartz, and leads to an increase in their dehydrating energy.

The authors reviewed the known methodical approaches to the determination of strength characteristics of rocks using their testing results. Some shortages of the approaches are revealed, and the common shortage is their empirical nature consisting in reduction of strength of rock mass in proportion to degradation of its quality. The proposed procedure to determine rock mass strength takes into account the rheological alteration of rock mass. The procedure better represents physical processes in mine openings due to rock pressure.

The article describes the lab test data on the structure and permeability of sand reinforced with elastic polyurethane. The electron microscopy reveals the spatial patterns of hard polyurethane, voids and mineral particles in reinforced sand. The permeability of the test samples is investigated under conditions of uniform triaxial compression. The response of permeability of reinforced rock to freeze-thaw is analyzed depending on moisture content, specific consumption of chemical reagents and reinforcement method. The stability values of the insulating properties of sand are compared for the cases of sand reinforcement by its mixing with polyurethane resin and through creation of a low-permeable inclusion (injection simulation). The advantage of injection over mixing is shown-the consumption of polymer composition is lower and the stability to seasonal temperature fluctuations is higher.

The article describes the method to estimate sensitivity of local seismic monitoring networks in two underground mines at the Khibiny Massif: Kirovsk and Rasvumchorr. The method uses empirical data of induced seismicity monitoring. At each monitoring station, based on the behavior of seismic waves and the distance to epicenters of seismic events, detection probability diagrams were plotted for seismic events and different ranges of seismic energies. The diagrams were used for plotting the probability of detection maps for a seismic event and a certain energy range. This approach has a few advantages. First, the input data may be records of production blasts and other sources rather than natural seismic events. Second, the method allows using the averaged probability diagrams for the decision-making on deployment and expansion of monitoring networks in mines. It is shown that monitoring networks ensure reliable recording probability (95%) only for the events with an energy higher than 10⁴ J; however, there is a potential of increasing the sensitivity and reliability of recoding events with an energy of 10² J in case of inclusion of additional monitoring stations.