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This study is aimed at investigating the mechanism by which a reactive material enhances the energy output of a composite charge consisting of an inner explosive, an intermediate non-detonating layer, and an outer explosive, which are widely used in tunable ammunition. Explosion experiments are conducted in two initiation modes. Using reactive Al/rubber significantly increases the fireball growth, shock wave velocity, and shock wave overpressure of the composite charge compared to using inert LiF/rubber. For simultaneous initiation, the increase is more obvious owing to the continuous exothermic reaction of the reactive layer. A composite charge with 40% (vol.) Al shows the highest difference in peak overpressure under the two initiation modes: 41.4%. A charge with 60% (vol.) Al ensures even lower shock wave and fireball velocities and peak overpressure than those of the 40% (vol.) Al charge, indicating that the excessive reactive Al content in the non-detonating layer inhibits the blast of the composite charge. [ABSTRACT FROM AUTHOR]

Mathematical modeling is applied to study the electrothermal explosion conditions of a gasless system surrounded by a dielectric medium. It is shown how conductive heat exchange intensity and Joule heating power affect the formation of dimensionless temperature and concentration profiles, the integral depth of transformation, and the reaction front propagation velocity. The stages of ignition and reaction propagation are divided using a criterion that assumes a conversion depth of 0.99 at any point in the sample. The amount of product formed at the ignition stage is determined. It is demonstrated that a large transformation depth is achieved near critical conditions during ignition on the axis of the sample, thereby causing the displacement of the ignition zone from the axis to the surface of the sample. [ABSTRACT FROM AUTHOR]

The aim of the article is to point out the dangers arising from the properties of plastic dust and what influence its properties have on the origin and course of the explosion. The present study deals with a sample of polyethylene dust, by-product of granulate production and storage. The explosion tests are performed on containers of a similar shape to those found in plants. The volumes of the closed vessels are 1.35 m3 (N1) and 5.45 m3 (N2). The tests are conducted in vessel N1 with a venting area DN 250 on the top of the vessel, in vessel N2 with a venting area DN 585 or DN 775 installed on the upper flanges of the vessels, and in vessels interconnected by pipes with a diameter DN 150 and length of 3, 6, and 10 m. The experiments show that the pressure of the explosion in technological equipment may reach higher values than those obtained in laboratory tests. During the explosion propagation in the connected vessels, the effect of overpressure appears due to precompression; as a result, the measured pressure and the rate of pressure rise are many times higher than the values measured only in the vessel itself with a venting area. As the explosion propagates from a larger volume vessel to a smaller volume vessel, the effect of precompression of the mixture increases the explosion parameters in the smaller vessel despite the opening areas of both vessels. Other elements can be also used to ensure sufficient explosion protection. The results also describe the effect of the length of the pipeline route by which the vessels are connected. [ABSTRACT FROM AUTHOR]

This paper presents the results of mathematical modeling of the propagation of air shock waves during methane explosion in mine workings taking into account their interaction with prefabricated parachute stoppings. Parachute stoppings are able to reduce the shock-wave intensity when the intensity of the incoming shock wave does not exceed the critical failure pressure of the stopping. The gas-dynamic method of calculating explosion-proof distances allows one to take into account parachute stoppings installed in various places of workings and to calculate the parameters of shock waves that have passed beyond the stopping. [ABSTRACT FROM AUTHOR]

Detonation overcompression during detonation convergence in a hemispherical charge of plastic-bonded triaminotrinitrobenzene with outer and inner radii of 75 and 20 mm after its initiation along the outer surface is studied. The experiment is numerically simulated with account for the transformation kinetics of an explosive into explosion products. The overcompressed detonation parameters in the explosive under study at a diagnosable charge radius of 20 mm are obtained via experiments and calculations: in the profile maximum, the pressure is 70 GPa, the front velocity is 9.45 km/s, and the mass velocity behind the front is 3.88 km/s. The overcompression achieved in the experiment under consideration is 2.3. The adiabat intersection point of the "nonreacting" explosive and its explosion products is revealed, which is implemented at a radius of 31 mm and a pressure of 52 GPa. The corresponding front velocity and the mass velocity behind the front at this point are 8.55 and 3.18 km/s. The resulting parameters at the adiabat intersection point are compared with the available literature data for triaminotrinitrobenzene and compositions based on it. A fairly large scatter of data is revealed. Suggestions are made about the causes of the scatter. [ABSTRACT FROM AUTHOR]

Values of the detonation velocity in thin layers of the VS-2 pyrotechnic composition are given. The Jones–Wilkins–Lee equation-of-state parameters of explosion products were determined. The obtained equation-of-state was used to perform numerical calculations, and the numerical results were compared with experimental parameters of the air shock wave resulting from the initiation of the VS-2 composition. Computational and experimental studies were carried out to determine the dependence of the pressure impulse on the thickness of the VS-2 layer. The dependence of the specific impulse of explosion products on the surface density of the VS-2 composition was determined. [ABSTRACT FROM AUTHOR]

To reveal the influence of vent parameters on the dynamic mechanism of an external explosion induced by a vented premixed methane–air explosion, the evolution process of an outdoor flow field under different vent opening pressures (), opening times (), and scaled vent size ( = ) is studied by methods of computational fluid dynamics. With an increase in , the shape of the unburned gas cloud and vented flame gradually changes from a jet shape to a depression toward the vent. The outdoor peak specific turbulent kinetic energy increases by 36.5 and 4 times with an increase in and , respectively. At = 0.1 s, the peak specific turbulent kinetic energy reaches 1411 m2/s2 and the turbulence range reaches 3 times the length of the room. With an increase in , , and , the occurrence time interval of the external explosion exhibits a decreasing trend. The external explosion is located at a distance of less than 1.4 times the length of the room. At = 0.05, the external explosion occurs at the furthest location. [ABSTRACT FROM AUTHOR]

In the present study, various test methods in the free field and confined explosions of cast HMX-based thermobaric explosives (TBX) and TNT are applied to quantify the explosion performance of TBX. The results show that the Mach reflection overpressure and impulse of TBX in the free field are much larger than those of TNT at the same relative distance from the explosion center. Based on the measured experimental data, semi-empirical formulas for calculating the overpressure at different distances from the TNT and TBX charges are derived. The fireball temperature and the duration of temperature higher than 1500°C of TBX are seen to be significantly greater. The measured peak pressure of the two explosives blast in an explosion tank are compared with the values predicted by modified calculation models, and the results are in good agreement. In addition, the quasi-static pressure generated by TBX in the explosion tank is 30.9% higher than that of TNT, which obviously reveals thermobaric effects of TBX. Based on the overpressure and quasi-static pressure calculation model, the TNT equivalents of TBX are calculated to correctly evaluate the TBX performance. The related contents in this paper will guide the formulation and performance assessment of TBX. [ABSTRACT FROM AUTHOR]

This study describes the mathematical modeling of an electrothermal explosion (ETE) of a gasless system placed in the annular layer of a conductive product. The influence of a change in the thermoelectric characteristics of a sample on the implementation, thermal conditions, and heat patterns of an ETE are considered. Based on the results obtained, the previously established experimental result about the anomalous effect of the electric heating power on the parameters of an ETE of a mixture of titanium and soot powders is explained. [ABSTRACT FROM AUTHOR]

In this paper, confined explosions of HMX-based aluminized explosives in a spherical chamber are studied. The effects of aluminum particles on the afterburning reaction and explosive performance are obtained by changing the size of the particles and the gas environment. The results show that the concentration of oxygen in air is not sufficient to support complete combustion of aluminum particles. The estimated oxidation rate of aluminum particles is 87–93%, and it tends to decrease with increasing particle size. Part of aluminum particles oxidize with detonation products, and the reaction can last for hundreds of microseconds. However, the degree of oxidation between the large-sized aluminum particles and detonation products is small. A new method is used to estimate the initial energy of detonation by observing the time difference between sensing the initial light and the pressure wave. This method leads to a conclusion that some of the aluminum particles are oxidized during detonation and provide additional energy to the primary blast wave. Small micron-sized aluminum particles in the range of 48.9 nm to 46.7 m extend the duration of the fireball. [ABSTRACT FROM AUTHOR]

A composite material based on the Ni–Al–C system is synthesized by the method of an electrothermal explosion at a pressure of 96 MPa. During the electrothermal explosion in a reactive powder medium (Ni + Al + C), a Ni- and Al-based melt is formed, in which carbon dissolves. In the process of crystallization of the final product, carbon, due to its low solubility in NiAl, is located on the surface of intermetallic grains of NiAl in the form of multilayer graphite nanofilms 50–80 nm thick and fills the intergranular space. The microhardness of the synthesized material is 3084 MPa. [ABSTRACT FROM AUTHOR]

Combustion and the formation of structures and phases in a 2Co–Ti–Al system during self-propagating high-temperature synthesis in a thermal explosion are under study. It is determined that a single-phase product (a Co2TiAl Geissler compound) can be obtained in this system. Morphology, microstructure, and physical-magnetic properties of combustion products of the system are investigated. [ABSTRACT FROM AUTHOR]

The results of diagnostics of thermal conditions of an electric thermal explosion (ETE) of a mixture of titanium and soot powders under quasistatic compression are presented. The effect of quasistatic compression pressure on the thermal and electrical parameters of an ETE is studied. It is shown that nonuniform heating occurs at low pressure, while uniform heating occurs at high pressure. A criterion is proposed for determining the thermal regime of the ETE of a heterogeneous mixture, based on the ratio of the exothermic interaction times and the electric current variation during a thermal explosion. It is established that the dependence of the electric current variation rate on time has one peak when the sample is heated nonuniformly and two peaks when it is heated uniformly. An abnormally low effective flash point of the heterogeneous titanium-soot mixture is explained. [ABSTRACT FROM AUTHOR]

The results of numerical simulation of the blast impulse of explosive charges on structural elements are presented. The numerical method was validated against available experimental data describing the blast effect in near-field explosion. Additional experiments on explosive acceleration of steel disks were performed. The effect of blasting conditions (the presence or absence of air, additional reflective surfaces) on the blast impulse was studied. [ABSTRACT FROM AUTHOR]

We have studied the effect of preload and the time delay in pressure application to the product of high-temperature synthesis by thermal explosion of a stoichiometric powder mixture on the grain size in the synthesized Ni3Al compound, on the nature of its fracture, strength, and ductility. [ABSTRACT FROM AUTHOR]

The experimental study of the high-temperature interaction kinetics of a titanium-soot mixture under quasistatic compression in an electrothermal explosion (ETE) is described. Dependences of the heating rate of a sample mixture on temperature are obtained, and the effective values of the energy of ignition activation and thermal explosion are calculated. The formation of the microstructure of intermediate and final interaction products is investigated. It is shown that the formation of a final product occurs according to a shell-core mechanism. The high rate of the solid-phase interaction of titanium and soot is explained by the formation of micropores and microcracks in the intermediate product, which ensure the high rate of surface diffusion of carbon. [ABSTRACT FROM AUTHOR]

The study of an electrothermal explosion (ETE) of a titanium—soot mixture under quasistatic compression is described. Experimental dependences of thermal and electric parameters of the ETE on the power of electric heating are obtained. It is shown that the heating rate of a reacting mixture significantly affects the ignition temperature and maximum temperature of the ETE. It is determined that, at the stage of pre-explosion heating, the electric resistance of the mixture decreases by 90—95%, and the rate of the temperature rise during a thermal explosion is independent of the heating rate of the mixture. A technique for determining the ignition time and temperature, based on measuring the thermal and electric parameters of the ETE. Liquid-phase and solid-phase interactions in the titanium—soot mixture powders are discussed. [ABSTRACT FROM AUTHOR]

The natural fracture of rock has a strong effect on the law of explosion stress wave transmission and crack propagation during blasting. Based on the stress wave theory, the influential mechanism for both the law of transmission of the stress wave and of crack propagation due to natural fracture and water jet slot are analysed. Next, an experiment is conducted to understand the crack propagation law because of the effect of an explosion shock wave, and the evolution law of the blast stress wave and blast-induced crack propagation is simulated by ANSYS/LS-DYNA. The results indicate that the existence of the water jet slot not only promotes the generation of the main crack along its direction, but also promotes the generation of the secondary crack near the water jet slot because of the explosion shock wave. The direction of propagation of the secondary crack and the main crack are seriously affected by the natural fracture. In addition, if the distance between the blast hole and the natural fracture is too small, a smash area is formed; and with an increase in the distance between the blast hole and the natural fracture, the smash area becomes smaller, and the effect on the blast-induced crack becomes weaker. [ABSTRACT FROM AUTHOR]

This study proposes a blast load model that generates multiple impulse curves with appropriate shapes depending on the scaled distance and, thus, precisely calculates the blast load distribution over the structure surface. The suitability of the proposed model is examined by using the finite element simulation of a blast test with steel plates and comparing the predicted deflections with the measurements. The results reveal that the proposed model accurately calculates the blast load distribution over the structure surface. The predicted deflection profiles of the steel plates are closer to the measured deflection profiles when the proposed model is employed, as compared to the existing models, which produce only a single impulse curve. [ABSTRACT FROM AUTHOR]

A key issue for explaining bursts and explosions of high explosives (HEs) under low-velocity mechanical impacts with registered time delays is the formation of local high-temperature regions. It is demonstrated by an example of HMX that the required temperatures should significantly exceed the HMX melting point and can be obtained only due to the work of viscosity forces in the liquid phase. In this case, however, it is necessary to ensure HE flow velocities greater than the primary impact velocities by several orders of magnitude. A mechanism of generation of such velocities is proposed: squeezing of the HE, which is heated on shear strains and plasticized, from the shear layer under the action of the pressure difference along the layer. Conditions of fast decomposition of the HE in the shear layer and conditions of an explosion of the surrounding HE are formulated. [ABSTRACT FROM AUTHOR]

Single-phase aluminum diboride was obtained by thermal explosion of an aluminum-boron mixture mechanically activated in a planetary ball mill. The additional mechanical treatment of the products of thermal explosion was found to reduce the coherent scattering area size of AlB2 to nanometer values. The results of x-ray phase and electron microscopy of the mechanocomposites and products of thermal explosion are presented. [ABSTRACT FROM AUTHOR]

The dynamic problems of the theory of combustion and explosion are classified from the point of view of competition of the characteristic times of bulk chemical reaction, frontal combustion, heat transfer, gas flow from the vessel, compression (motion of the piston), and heating (cooling) rate. We consider dynamic similarity criteria such as the ratio of the characteristic times in problems of classical thermal explosion, dynamic thermal explosion, flammability limits, combustion in communicating vessels, competition of frontal and volumetric combustion, autoignition by adiabatic compression, competition of frontal combustion and piston motion, as well as compound similarity criteria (such as functions of simple dynamic similarity criteria). The problem of autoignition of a mixture by compression is considered, and a method for obtaining an analytical solution of the problem and an algorithm for the approximate solution based on a special differential criterion are proposed. [ABSTRACT FROM AUTHOR]

Self-propagating high-temperature synthesis in both the modes of both layer-by-layer combustion and dynamic thermal explosion was carried out using preliminary mechanical activation of BC-Ti powder mixtures in a planetary ball mill. Preliminary mechanical activation conditions of reaction mixtures that provide a reduction in the reaction initiation temperature to 600 ± 20◦C were determined. The reaction products consist of mixtures of TiC and TiB with submicron grain size. The results of x-ray diffraction and electron microscopy studies of activated samples and reaction products are presented. [ABSTRACT FROM AUTHOR]

Interaction of an expanding shock wave with a layer of particles having a rough surface is considered within the framework of the collisional model of a gas suspension. The influence of roughness on the shape of the contact boundaries in the gas phase and on the boundaries of the cloud of particles is analyzed. The development of the Richtmyer-Meshkov instability is demonstrated. Factors of particle dispersion are determined. Instability evolution is found to increase the amplitude of surface disturbances, and the development of collision dynamics favors smearing of finger-type structures. If the particle motion is essentially random, the pattern of cloud spreading is similar to that observed in experiments. [ABSTRACT FROM AUTHOR]

A method is proposed for determining the energy release in a combustible mixture, which is based on processing the trajectory of the expanding wave from the viewpoint of the strong explosion model. The wave trajectory in the case of critical initiation of multifront detonation in a combustible mixture is compared with the trajectory of a blast wave generated by the same initiator in an inert mixture whose gas-dynamic parameters are equivalent to those of the combustible mixture. The energy release is defined as the difference between the joint energy release of the initiator and combustible mixture in the case of critical initiation and the energy release of the initiator in the case of blast wave excitation in the inert mixture. Results of experimental validation of the method by an example of a stoichiometric acetylene-oxygen mixture are presented. Noticeable deviations of the experimental profile of energy release from available model concepts are observed. [ABSTRACT FROM AUTHOR]

This paper describes the measurement results for the shock wave propagation during an explosion of an explosive material with plastic filler. The detection is carried out with the help of high-speed analog and digital video cameras. The air shock wave is visualized by means of shadow photography in transmitted light in the zone of separation from expanding explosion products and using a background oriented schlieren method in the far zone. The optical measurements of the air shock wave propagation are used to estimate a maximum pressure in the compression zone at different sections and compared with the data obtained by the pressure gauges. The calculated pressure peaks are in good agreement with the measured ones. The background oriented schlieren method proves to be a useful tool easily introduced in conventional large-scale polygon experiments. [ABSTRACT FROM AUTHOR]

Results of modeling the propagation of a shock wave formed by an explosion of a spherical charge of a high explosive in a semi-infinite space bounded by a flat substrate are reported. Problems of the action of such a wave on objects rigidly fixed on the substrate (a single prism and a set of prisms simulating an urban area) are considered. The computations are performed in a three-dimensional inviscid formulation with the use of the AUTODYN module of the ANSYS commercial software package. These numerical predictions are compared with experimental data on the static pressure measured by sensors mounted on the prism walls. It is demonstrated that an adequate description of the unsteady flow pattern formed around the obstacles mounted on the substrate can be provided. Based on these numerical data, the intensity of the shock wave action on various objects is estimated. [ABSTRACT FROM AUTHOR]

The spectral-kinetic characteristics of luminescence of PETN with iron nanoparticle inclusions are measured in real time in the case of a laser initiated explosion (the wavelength is 1064 nm, and the pulse duration is 14 ns). During the action of the laser radiation pulse, the luminescence of the samples is observed, and the explosive decomposition occurs in a microsecond time interval. The spectral pyrometry method is used to establish the thermal nature of explosive luminescence. The explosion temperature is estimated to be 3400 ±100 K. [ABSTRACT FROM AUTHOR]

Issues of explosion and fire safety of silane during its transportation and storage are intimately related to its possible catastrophic leak off from tanks if they become cracked. It turned out that silane self-ignition is possible at some leak off velocities. The interest of the aerospace industry to problems of ignition and combustion of silane combined with other fuels should be also noted. Experimental investigations of such problems, which are rather expensive and laborconsuming, provide primary information for the development and verification of mathematical models of physical and chemical processes, capable of predicting the characteristics of silane mixing, ignition, and combustion induced by its exhaustion. Recent experiments of Prof. Chen and his colleagues from Taiwan allowed them to determine the critical length of the silane jet (distance from the tube exit where ignition of exhausting silane occurred) and the time of silane ignition. In the present work, an attempt is made to simulate these phenomena within the framework of the concept of the critical concentration of silane with studying the dynamics of silane leak off from a tube. [ABSTRACT FROM AUTHOR]

The interaction between natural convection and the heat explosion in porous media is studied. The model consists of a nonlinear heat equation coupled with the Darcy equation for the motion of an incompressible fluid in a porous medium. Numerical simulations are performed using the alternate direction finite difference method and the fast Fourier transform method. A complex behavior of solutions is observed, including periodic and aperiodic oscillations and an oscillating heat explosion. It is shown that convection can decrease the risk of the explosion due to additional mixing and heat loss, but it can also facilitate the explosion due to temperature oscillations arising as a result of instability of stationary convective regimes. [ABSTRACT FROM AUTHOR]

This paper presents the results of two large-scale tests performed to clarify the conditions for the detonation of propane-air compositions in model surface clouds in the absence and in the presence of confining rigid walls. Model clouds with dimensions of 15 × 6 × 4.2 and 15 × 6 × 2 m were confined by plastic tents. A mixture of the starting reagents in the cloud was ignited by hot detonation products propagating along a perforated ø0.82 × 23 m tube passing through the space of the tent. Hot detonation products were injected from the tube through holes of 20 and 40 mm diameters. Detonation of the propane-air mixture in the tube was initiated by explosion of an explosive charge placed at the tube end. Detonation occurred in the propane-air cloud bounded on one side by a rigid vertical wall, and no detonation was observed in the cloud with similar injection of hot products without a rigid wall. It is concluded that the divergence or convergence of the flows of hot detonation products plays a key role in the process, being responsible for the presence or absence of detonation, respectively, in the mixing region. [ABSTRACT FROM AUTHOR]

Explosion characteristics of PMMA particles with three different diameters (100 nm, 800 nm, and 30 μm) are studied experimentally. The explosion severity including the maximum explosion pressure and the pressure rise rate of 100-nm PMMA particles significantly exceed those of 800-nm and 30-μm PMMA particles at low concentrations due to a greater specific surface area. However, the explosion severity of 100-nm PMMA particles gradually decreases below that of 800-nm PMMA particles once the dust concentration reaches 250 g/m and above because 100-nm PMMA particles are prone to agglomerate, but it is still higher than that of 30-μm PMMA particles. In addition, the maximum explosion pressures increase with increasing concentrations of PMMA particles of all sizes, peaking at 250 g/m, while they do not change significantly as the concentrations go beyond 500 g/m. According to the explosion classification based on the deflagration index, nano-PMMA particles indicate a higher explosion risk and more serious explosion severity than those of micro-particles. [ABSTRACT FROM AUTHOR]

The effect of preliminary mechanical activation of low-calorific-value powdered formulations in a planetary ball mill on the main parameters of the subsequent thermal explosion has been studied. It has been found that in mechanically activated compositions, the initiation temperature of thermal explosion is reduced by hundreds of degrees. The maximum decrease (1300°C) is observed for the Ti + 4 wt.% C system. Regimes of preliminary mechanical activation of reaction mixtures and the subsequent thermal explosion conditions producing TiAl and NiAl single-phase intermetallic compounds with nanometer grain size were determined. For the 3Ni + Al composition, the energy accumulated during mechanical activation was evaluated. It is shown that the initiation temperature of thermal explosion in the MA compositions studied can be used to estimate the temperature that develops in the mill drums. [ABSTRACT FROM AUTHOR]

A thermal explosion and self-propagating high-temperature synthesis in low-calorific SiO-Al mixtures subjected to preliminary mechanical activation are obtained. Results of x-ray and electron-microscopic investigations of the microstructure and phase composition of activated mixtures and reaction products are reported. It is found that complete reduction of quartz by aluminum occurs only in the thermal explosion mode. [ABSTRACT FROM AUTHOR]

A thermal explosion synthesis method for production of magnesium diboride, MgB, has been investigated, revealing the formation of a high-quality material via an exothermic reaction after heating a mixture of magnesium and boron powders to a temperature of ≈600°C. The reaction product has been characterized by different thermal and x-ray analyses. It has been also revealed that aluminum diboride, AlB, is not formed from aluminum and boron powders in the range of temperatures applied. [ABSTRACT FROM AUTHOR]

A physicomathematical model of shock wave initiation of an explosion of oxygen-containing bubbles in liquid hydrocarbon fuels is developed. The model is used to calculate an explosion of bubbles in which the initial concentration of fuel vapors is outside the flammability limits. A principal possibility of condensation of fuel vapors during compression of a fuel-rich bubble located in liquid cyclohexane with a comparatively high initial temperature is demonstrated. Condensation leads to a decrease in the fuel concentration in the gas lower than the fuel-rich flammability limit. As a result, an explosion of an initially non-combustible bubble becomes possible. The condensation rate is estimated. It is found to be sufficiently high to change the chemical composition of the gas during the period of the first oscillation of the bubble. The explosion limits of the bubble are calculated as functions of the initial pressure, temperature, and amplitude of the shock wave. If condensation is taken into account, the explosion limits are expanded. Bubble liquids (2-ethylhexanol and isopropyl benzene) where the fuel vapor concentration is initially lower than the fuel-lean flammability limit are considered. It is shown that liquid evaporation induced by mechanical mixing of the phases can shift the chemical composition of the gas inward the flammability region, resulting in a bubble explosion with a corresponding increase in gas temperature. Calculated and experimental results are found to be in good agreement. Explosive processes in bubble media containing a liquid monopropellant are considered at the qualitative level for the first time. An assumption is put forward about a possibility of multiple explosions of an individual bubble loaded by a series of shock waves and subjected to multiple transitions of the detonation wave over the liquid with distributed bubbles, which may be used for generating a series of powerful acoustic signals in the ambient space. [ABSTRACT FROM AUTHOR]

In this paper, we study a micro-hotspot model for the laser initiation of explosive decomposition taking into account the melting of the matrix of the energetic material and the nanometallic inclusion contained in its volume. The heating features of the nanoparticle in an inert matrix are investigated, and the dependence of the maximum temperature on the surface of the inclusion on its radius is constructed. It is shown that melting leads to a reduction in the maximum heating temperature and a slight change in the radius of the most heated nanoparticle. The dependences of the critical initiation energy density of explosive decomposition of pentaerythritol tetranitrate (PETN) with aluminum nanoparticles on the inclusion radius with and without melting are calculated. With melting taken into account, the model gives higher critical initiation energy density of explosive decomposition. In the case of inclusions of large radius, the formation of the reaction site of explosive decomposition occurs before complete melting of the metal inclusion, which results in solidification of the melt during the induction period. [ABSTRACT FROM AUTHOR]

The propellant performance and the velocity of expansion of detonation products of explosives based on RDX and HMX and their mixtures with particulate Al were investigated. Measurements were performed in air at atmospheric pressure and in rarefied air. Comparison of the results shows that the detonation products of explosives, including those containing no Al additives, react with the surrounding air. The completeness of the reaction increases with increasing velocity of detonation products in air. [ABSTRACT FROM AUTHOR]

The problem of thermal explosion in a semi-batch reactor is solved. The critical conditions for the thermal explosion are studied. It is shown that the ignition resulting from the chemical reaction is possible both during the stage of feeding of the second reactant solution and after its completion. The dynamic behavior of the reactor depending on the temperature of the heat exchanger and the volumetric feed rate of the second reactant is analyzed. It is shown that ignition at the feeding stage occurs at high temperature of the heat exchanger and involves two macroscopic stages. In the first stage, the temperature increases with increasing rate (thermal explosion regime), and in the second stage, its further increase occurs in the regime of combustion of the second reactant. The critical ignition conditions are found to be independent on the feed rate of the second reactant in a particular range of its values. [ABSTRACT FROM AUTHOR]

The explosion wave overpressure and the flame propagation velocity of the gas explosion in a bifurcating duct are experimentally measured and theoretically analyzed. The results show that the effect of the bifurcation on the flame velocity and overpressure is obvious. Especially, the explosion wave overpressure and the flame propagation velocity increase sharply at the bifurcation point, and the surface at the bifurcation location is destroyed seriously. The gas explosion propagation is verified to suffer a dual effect of sudden expansion of the area and obstruction induction. [ABSTRACT FROM AUTHOR]

The paper focuses on the application of mathematical modeling of methane turbulent combustion in a complex geometry and on the choice of parameters of one-step and two-step chemical kinetics models. Parameters of chemical kinetics have a profound influence on the correct implementation of the combustion mathematical model used in the CFD (computational fluid dynamics) simulation of the methane-air mixture explosion in a family house. Results are compared with experimental measurements. [ABSTRACT FROM AUTHOR]

Experimental data on the properties of explosion products in overdriven detonation for 50/50 TNT/RDX and PBX-9502 explosives indicate conditions characterized by a negative Grüneisen parameter. Given a possible relationship of this anomaly with the properties of explosion product components, available experimental data for nitrogen, carbon monoxide, carbon dioxide, and water are analyzed. The first three of these (carbon dioxide specifically) are capable of manifesting a negative Grüneisen parameter at pressures and temperatures characteristic of the anomaly of overdriven explosion products. [ABSTRACT FROM AUTHOR]

In this paper, the application of emulsion explosives in synthesizing nanostructured ceria is introduced. The reaction mechanism to prepare nanostructured ceria with emulsion explosives by the detonation synthesis method is discussed. Nanostructured ceria powder is prepared by initiating special emulsion explosives in which Ce(NO)·6HO is regarded as the main oxidant in an explosion containment vessel. The phase composition, crystallite form, morphology, and microstructure of the as-synthesized products are characterized by x-ray diffraction analysis and transmission electron microscopy. The Brunauer-Emmett-Teller method is used to measure the specific surface areas of the powders. Nanostructured ceria belongs to the cubic phase. The morphology of as-synthesized ceria is nearly spherical, and the mean size of ceria particles is 55 nm. It is a mixture of monocrystal and polycrystal grains. [ABSTRACT FROM AUTHOR]

CO-laser welding of 12Kh18N10T stainless steel and a VT1-0 titanium alloy with the use of a composite insert obtained by means of explosive welding of four sheets (VT1-0 titanium, high-purity tantalum, M1 copper, and 12Kh18N10T steel) is experimentally studied. After mechanical processing, the insert is placed between the welded steel and titanium sheets. Butt-end welding of the steel and titanium sheets with the steel and titanium sides of the insert, respectively, is performed by a laser beam. Metallographic and spectrographic investigations are performed; mechanical properties of the resultant composite are tested. After thermal processing, the composite is found to break over the copper layer, which has a strength of 417 MPa. [ABSTRACT FROM AUTHOR]

Critical densities of the energy of laser initiation of PETN containing nanoscale aluminum inclusions at radiation wavelengths of 1064 and 532 nm were measured experimentally. The critical initiation-energy density that corresponds to a 50%th probability of explosion was 1.15 J/cm for the first harmonic of a neodymium laser and 0.7 J/cm for the second. The dependence of the efficiency of radiation absorption by aluminum on the size of metal nanoparticles for the first and second harmonics of a neodymium laser is calculated. It is shown that the particle diameter corresponding to the absorption efficiency maximum and the amplitude of the maximum depend on the radiation wavelength. The absorption efficiency maximum for the first harmonic is observed in an inclusion 204 nm in diameter, and for the second, in an inclusion 96 nm in diameter. The amplitude of the maximum increases from 0.351 at a wavelength of 1064 nm to 0.490 at a wavelength of 532 nm. Dependences of the critical initiation energy density for energetic materials on the radius of metallic nanoparticles are calculated. Qualitative agreement between theoretical and experimental results is shown. [ABSTRACT FROM AUTHOR]

The applied pressure resulting in an explosion in the case of shock-induced shear is demonstrated to depend on the shear area [area of the contact of the high explosive (HE) with the metal surface]. The dependence of the probability of an explosion of the HE (phlegmatized HMX and PETN) compressed between two steel plates (end faces of two rollers) on the applied pressure and the contact area of the HE with the upper roller is confirmed in experiments on sensitivity to friction under shock-induced shear. The upper roller is shifted by 1.5 mm. It is demonstrated that an increase in the area of the shock-pressed HE contact with the roller increases the probability of the HE explosion under shock-induced shear of the upper roller at identical pressures applied to the HE. A scale factor of the influence of the HE/roller surface contact area on the pressure at which the HE explosion occurs under shock-induced shear of the surface contacting the HE is found. It is shown by statistical methods that the pressure leading to the HE explosion under shock-induced shear of the adjacent steel surface with respect to the HE is distributed in accordance with Weibull's two-parameter law. [ABSTRACT FROM AUTHOR]

Interaction of a single chemically active bubble in water with acoustic waves is numerically studied within the framework of the model of a two-dimensional unsteady flow of an ideal compressible medium. The boundaries between the phases are explicitly identified. It is demonstrated that bubble explosion initiation can be determined by the character of bubble deformation. Nonsphericity of deformation and jet formation lead to an explosion even if the bubble does not collapse. The possibility of the bubble explosion in an expansion wave, transfer of detonation from one bubble to another, and, thus, emergence of bubble detonation is demonstrated. [ABSTRACT FROM AUTHOR]

Measurements of turbulent burning velocities in fan-stirred explosion bombs show an initial linear increase with the fan speed and RMS turbulent velocity. The line then bends over to form a plateau of high values around the maximum attainable burning velocity. A further increase in fan speed leads to the eventual complete quenching of the flame due to increasing localised extinctions because of the flame stretch rate. The greater the Markstein number, the more readily does flame quenching occur. Flame propagation along a duct closed at one end, with and without baffles to increase the turbulence, is subjected to a one-dimensional analysis. The flame, initiated at the closed end of the long duct, accelerates by the turbulent feedback mechanism, creating a shock wave ahead of it, until the maximum turbulent burning velocity for the mixture is attained. With the confining walls, the mixture is compressed between the flame and the shock plane up to the point where it might autoignite. This can be followed by a deflagration to detonation transition. The maximum shock intensity occurs with the maximum attainable turbulent burning velocity, and this defines the limit for autoignition of the mixture. For more reactive mixtures, autoignition can occur at turbulent burning velocities that are less than the maximum attainable one. Autoignition can be followed by quasi-detonation or fully developed detonation. The stability of ensuing detonations is discussed, along with the conditions that may lead to their extinction. [ABSTRACT FROM AUTHOR]

Parameters of detonation waves in homogeneous and heterogeneous high explosives are registered. Dependences of the duration of the chemical reaction zone on the critical diameter are obtained. The transition from a stable to an unstable detonation mode in liquid explosives is studied. In these studies, the regime of normal detonation with a stretched shock wave is observed, and the induction period of the thermal explosion is determined. [ABSTRACT FROM AUTHOR]

A study was made of the explosion probability and the pressure of explosive decomposition products of PETN samples of density 1.73 g/cm with different contents of Al nanoparticles under pulsed laser irradiation (1060 nm; 20 ns). It was experimentally found that the maximum sensitivity and maximum pressure of explosion products are obtained when the mass concentration of nanoparticles is 0.1%. In this case, the mixture sensitivity increases by factor of ≈100 with respect to the samples containing no nanoparticles. The observed effect is due to radiation absorption directly by nanoparticles with the formation of 'hot spots,' which initiates an exothermic reaction in the main substance. It is shown that the addition of 0.1% Al decreases the impact sensitivity with respect to the samples without additives. This makes it possible to consider this mixture as a promising material for optical detonators. [ABSTRACT FROM AUTHOR]