Relation between the critical detonation diameter of explosive charges with characteristics of their shock-wave sensitivity

Correlation dependences between the critical diameter of high explosive (HE) charges and characteristics of their shock-wave sensitivity are theoretically justified. Relations for the critical radius of curvature of the detonation-wave front and for the critical detonation diameter are derived on the basis of the author’s theory of the critical diameter and the generalized kinetic characteristic of HE decomposition determined from the experimental dependence of the distance of transition of the initiating shock wave to the detonation wave on the wave amplitude. A qualitative analysis of these relations reveals good agreement with available experimental data. Key words: detonation, critical diameter, sensitivity, shock-wave initiation of detonation, HE decomposition kinetics. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 101–105, May–June, 2009.     

Nonclassical steady-state detonation regimes in pressed TNETB

The reaction zones and the dependence of the velocity of steady-state detonation waves on the initial density of pressed TNETB are studied using a VISAR interferometer. It is shown that, in the range of initial densities of TNETB 1.56–1.77 g/cm³, the propagation of a steady-state detonation wave is possible without the range of elevated pressures (chemical spike) in the reaction zone predicted by the classical theory. The dependence of the detonation velocity on the initial density shows singularities which indicate that a steady-state underdriven regime can occur in this range of initial densities. Based on the well-known theoretical concepts of the hot-spot decomposition mechanism of heterogeneous explosives, it is shown that the possibility of the existence of a steady-state detonation wave without a chemical spike, in particular, underdriven detonation, and the effect of the internal structure of the charge on the detonation regime are explained by the decomposition of explosives at the shock-wave front. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 97–103, November–December, 2007.     

Influence of the initial gas pressure on the detonation limits and parameters of low-density secondary explosives in an inert porous medium

This paper reports the results of an experimental study of the detonation of low-density (3–40 mg/cm³) secondary high explosives (HEs) in evacuated and gas-filled inert porous media. A convective-jet mechanism of detonation propagation was found to occur under all conditions studied. The effects of the type of HE and initial gas pressure on the critical density of the HE and detonation parameters were elucidated. It is shown that, in the presence of air, detonation can occur at a lower volume-averaged density of the HE than in the case of the evacuated media and there are two limits (minimal and maximal) for the initial gas pressure. As the volume-averaged density HE decreases, the limits approach each other and, for a certain critical density of the HE, detonation exists only at one value of the initial pressure. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 106–117, May–June, 2009.     

Conditions of detonation initiation by focusing shock waves in a combustible gas mixture

Based on experiments on focusing shock waves in hydrogen-air mixtures and available publications, the critical shock-wave Mach number at which detonation is initiated near the apex of a concave reflector is analyzed as a function of the reflector size and reactivity of the mixture. The effect of the reflector shape and size on the value of this Mach number is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 84–89, November–December, 2007.     

Detonation Velocity of Emulsion Explosives Containing Cenospheres

The detonation velocity of an emulsion explosive containing hollow alumosilicate microspheres (cenospheres) as the sensitizer is measured. The size of the microspheres is 50–250 μm. The relations between the detonation velocity and the charge density and diameter are compared for emulsion explosives containing cenospheres or glass microballoons as the sensitizer. It is shown that for a 55 mm diameter charge, the maximum detonation velocity of the composition with cenospheres of size 70–100 μm is 5.5–5.6 km/sec, as well as for 3M glass microballoons. The critical diameter for the emulsion explosive with cenosphere is 1.5–2 times larger than that for the emulsion explosive with glass microballoons and is 35–40 mm. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 119–127, September–October, 2005.     

Physical model for shock-wave initiation of detonation of plastic-bounded TATB-based explosive

A physical model for the macrokinetics of shock-wave initiation of detonation in plastic-bounded TATB-based explosive is proposed that is based on the assumption of electronic energy transfer from hot spots. Results of numerical modeling of experiments on shock-wave initiation of detonation of LX-17 are presented. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 117–126, September–October, 2006.     

Structure and initiation of plane detonation waves in a bidisperse gas suspension of aluminum particles

Initiation and propagation of plane waves of heterogeneous detonation in a stoichiometric suspension of two fractions of aluminum particles in oxygen are analyzed numerically. It is found that the detonation is not ideal, and the steady-state part of the shock-wave structure is bounded by an equilibrium frozen sonic point. Initiation criteria depend on the particle-size distribution of the mixture. Initiation by explosive shock waves can lead to formation of unstable two-front structures. Addition of a small amount of fine particles into the discrete phase allows the initiation energy to be substantially reduced. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 46–55, March–April, 2008.     

Modeling of weakly nonideal detonation of condensed high explosives with a high content of carbon

A numerical model of weakly nonideal detonation of plastic-bounded TATB is proposed, which alleviates the requirements to the computational grid and necessary computational resources. The model is tested against the experimental results on the dependence of the detonation velocity on the charge diameter and detonation propagation in an annular charge. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 56–60, March–April, 2008.     

Energy release of mixed explosives during propagation of a nonideal detonation under conditions similar to the operation conditions of a blasthole charge

Detonation experiments were performed in a specially developed explosive device simulating a blasthole using charges of fine-grained and coarse-grained (granular) 30/70 TNT/ammonium nitrate mixtures of identical density 0.89 g/cm³ in steel shells with an inner diameter of 28 mm and a wall thickness of 3 mm at detonation velocities of 4.13 and 2.13 km/sec, respectively. Despite significant differences in detonation velocity (pressure), identical expansion of the charge shells was observed. On the other hand, numerical simulations of detonation propagation in the explosive device with the corresponding velocities ignoring the possibility of energy release behind the shock front show that the expansion of the charge shell is always greater in the case of a high-velocity regime. It is concluded that under the conditions simulating detonation propagation and the work of explosion products in a blasthole, effective additional energy release occurs behind the low-velocity (nonideal) detonation front. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 111–120, July–August, 2007.     

On the Hydrodynamic Thickness of Cellular Detonations

The characterization of the detonation dynamic parameters (detonability limits, direct initiation energy, critical tube diameter, etc.) requires a characteristic length scale for the detonation wave in the direction of propagation. However, most detonations are unstable, their reaction zones are turbulent, and their structure departs significantly from the idealized one-dimensional Zel'dovich-Von Neumann-Doring model. It is argued that the most suitable length scale to characterize a turbulent detonation wave is the location of the sonic surface, which separates the statistically stationary flow of the reaction zone structure from the unsteady expansions behind the wave. Previous real and numerical experiments are reviewed in order to determine the relation between the global location of the mean sonic surface and the chemical, mechanical, and thermodynamic relaxation processes occurring in the detonation wave structure. Based on the experimental evidence, we postulate that the structure of turbulent detonations can be modeled in the one-dimensional Zel'dovich-Neumann-Doring framework, with the turbulence effects as source terms in the momentum and energy equations. These source terms involve the relaxation rates for the mechanical fluctuations, thermal fluctuations and the chemical exothermicity towards equilibrium. In the framework of the idealized one-dimensional structure with source terms, the sonic surface location is governed by the balance between the competing source terms satisfying the generalized Chapman-Jouguet criterion. We recommend that future work in detonation research should be focused at: 1) acquiring a large experimental database for the mean detonation properties (detonation velocity, location of sonic surface and mean reaction zone profiles); 2) the development of the appropriate source terms involving the turbulent fluctuations in the averaged equations of motion. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 157–180, November–December, 2005.     

Structure of detonation waves in tetranitromethane and its mixtures with methanol

A VISAR laser interferometer was used to measure mass velocity profiles in steady-state detonation waves in tetranitromethane and its mixtures with methanol. In the experiments with tetranitromethane, the chemical-spike pressure was found to be 1.7 times higher than the Chapman-Jouguet pressure. In mixtures with nearly stoichiometric methanol concentrations, the detonation front remained stable, but the chemical-spike amplitude increased suddenly and the shock broadened, probably due to the decomposition of the explosive at the front. A 50% increase in methanol concentration led to instability of the detonation front manifested in oscillations in the mass velocity profiles. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 95–100, May–June, 2009.     

Theory of solid-state detonation

The Jouguet theory allows one to estimate the detonation velocity from the known shock adiabat of the product of a solid-state chemical reaction initiated by a shock wave. Using manganese and zinc chalcogenides as an example, it is shown that such estimates are close to experimental detonation velocities in these systems. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 108–110, March–April, 2007.     

Numerical modeling of TATB shock-wave heating

A model of shock-wave heating of condensed high-explosives (HE) in which a refined dependence of the heat capacity of an HE on temperature is used and the effect of the initial density of the HE is taken into account is given. The dependences of HE (TNT, PETN, and TATB) heating on pressure in the shock-wave front are calculated. Modeling of TATB heating is of interest for understanding the shock-wave detonation initiation, including the dependence of the shock-wave sensitivity on the initial density and temperature of an HE. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 94–99, March–April, 2000.     

Density dependence of detonation velocity for some explosives

The nonmonotonic dependence of the detonation velocity of a cylindrical charge on density for explosives of the 2nd type is due to the effect of the finite charge diameter and is related to an increase in the width of the reaction zone with a reduction in the porosity of the explosive. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 116–124, July–August, 2006.     

Bubble detonation conditions

Initiation of bubble detonation in the system “inert liquid-explosive gas bubbles” by a detonation wave in a gas was studied experimentally. Compression-wave pressure profiles were determined as functions of the length of the initiation section and the initial pressure of the explosive gas mixture in it. It was shown that because of the effect of the explosive-gas volume between the diaphragm and the upper boundary of the bubble medium, the pressure in front of the initiating wave increased much more slowly than the initial pressure. The optimal length of the initiation section was found, and the critical (minimum) initiation pressure in it and at the shock-wave front were determined. It was found that for a fixed gas volume concentration in the bubble medium, the pressure in the initiation section increased insignificantly as the length of the section decreased. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 84–90, March–April, 2007.     

可变形战斗部主辅装药殉爆研究

为确定主辅装药的选型原则，对主装药在两种辅装药滑移爆轰作用下的动态响应过程进行了数值仿真研究，着重考察了辅装药爆轰性能和主辅装药间的隔爆层对冲击波衰减的影响，并结合非均质炸药的冲击起爆临界能量判据，得到传人主装药内的脉冲压力和脉冲持续时间。结果表明，引起主装药殉爆的主要因素是主装药的爆轰感度和辅装药的爆轰压力，隔爆层位置应位于辅装药和外壳体之间。     

Discoveries in Detonation of Molecular Condensed Explosives in the 20th Century

A number of experimental results that could not be satisfactorily explained within the framework of the Grib—Zel'dovich—Neumann—Döring detonation theory are reviewed, namely, the oscillating detonation of some liquid high explosives (HE), the weak dependence of the time of detonation transformation of heterogeneous charges on their structure (particle size, liquid or solid state, etc.) with a strong dependence of the critical diameter of detonation on the structure, and the extremely weak dependence of the detonation rate of liquid HE on the charge diameter with a significant value of the critical diameter of detonation. These studies yielded the following results: 1) for each heterogeneous HE, a typical shock–wave pressure p ^* and a typical initial density ₀ ^* were found, such that, for their low values, HE transformation follows the mechanism of hot points (depends on the charge structure), and for high values of these parameters, HE transformation obeys the homogeneous mechanism (does not depend on the charge structure); 2) two new theoretical notions were discovered and used in the detonation theory: the phenomenon of breakdown of the chemical reaction in the shock–wave front by rarefaction waves and the notion of a shock jump, which reflects the specific character of action of shock waves on complex multiatomic molecules of condensed HE. It was also shown that the discovery of the parameters p ^* and ₀ ^* and the breakdown and shock jump phenomena allowed one to confirm experimentally the explanations of the above observations, which are incompatible with the Grib—Zel'dovich—Neumann—Döring detonation theory, to propose the structure of the front of detonation waves both in homogeneous (stable and oscillating) and heterogeneous HE whose basic property is HE transformation (partial or complete depending on the HE power and initial density) already in the shock–wave front, and to proposed principally new ideas on the nature of the critical diameter of detonation of homogeneous and heterogeneous HE.     

Detonation of pressed HMX charges

The pressure-profile measurement results obtained in the shock-wave front in bromoform upon detonation of HMX charges of diameter 40 mm and length 22–110 mm are reported. The initial density of the charges was 1.81 g/cm³. In all the experiments, a monotonic decrease in pressure occurred, and a chemical peak was not observed. With increase in the charge length, the maximum pressure values first increase and then decrease. An analysis of the pressure measurement results shows that, for the given charge size and the initiation system used, the process of HMX detonation occurs in a nonstationary regime. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 83–86, July–August, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 97-03-32000).     

Reliability of kinetic data used for estimating multifront detonation parameters

A faster increase in the cell size and other important parameters of multifront detonation than that predicted by kinetic calculations is obtained for fuel-oxygen mixtures of hydrogen and typical hydrocarbons diluted by nitrogen. In a stoichiometric hydrogen-oxygen mixture diluted by an additional amount of oxygen or hydrogen, experimental and calculated data are also found to diverge with increasing concentration of the added species. This effect, however, is not observed if these mixtures are diluted by helium or argon. An assumption about the reason for this difference in data is put forward. A conclusion is made that kinetic data should be corrected as applied to detonation conditions. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 89–94, May–June, 2009.     

Effect of the degree of dispersion on the detonation wave structure in pressed TNETB

A VISAR interferometer was used to study the reaction zone in steady-state detonation waves in pressed TNETB at different initial densities (1.23–1.71 g/cm³) and degrees of dispersion (5 and 80 μm) of the initial powdered high explosive (HE). The initial density range in which a pressure rise was observed instead of the theoretically predicted chemical spike is shown to depend on the degree of dispersion of the HE. The unusual change in the parameters in the reaction zone is explained by the heterogeneous structure of pressed HEs, whose decomposition has a local nature and proceeds partially at the compression wave front. A technique for recording wave profiles using LiF windows was developed, which confirmed that all qualitative features observed when using aluminum foils ≈200 μm thick and a water window reliably reflect the detonation wave structure. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 90–95, September–October, 2007.