Home – Home – Jornals – Advanced Search

Self-propagating high temperature synthesis in both the layer-by-layer combustion mode and the dynamic thermal explosion mode was carried out using preliminary mechanical activation of B₄C-Ti powder mixtures in a planetary ball mill. Preliminary mechanical activation modes of reaction mixtures were determined that provide a reduction in the reaction initiation temperature to 600±20 gr. The reaction products consist of mixtures of TiC and TiB₂ with submicron grain size. The results of X-ray diffraction and electron microscopy studies of activated samples and reaction products are presented.

This paper presents an experimental study of heat and mass transfer and phase transformation in the suppression of flaming combustion and thermal decomposition of model ground, crown, and combined forest fires due to the local action of water. The experiments were carried out with typical combustible forest materials (mixture of leaves, needles, and twigs) and models of trunks and branches of trees. The conditions and characteristics of suppression of flaming combustion and the thermal decomposition of combustible forest materials were determined. It is shown that in the case of crown and combined fires, local short-term (a few seconds) action of a liquid projectile does not lead to suppression of thermal decomposition of material (only localization of flaming combustion is possible). In the case of ground forest fires, this approach may be effective with an appropriate choice of the area of the combustion zone sprayed with water and the spraying intensity and time.

This paper describes the measurement results for the shock wave propagation during an explosion of an explosive material with plastic filler. The detection was carried out with the help of high-speed analog and digital video cameras. The air shock wave was visualized by means of shadow photography in transmitted light in the region of separation from expanding explosion products and using a background oriented Schlieren method in the far region. The optical measurements of the air shock wave propagation were 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 were in good agreement with the measured ones. The background oriented Schlieren method proved to be a useful tool easily introduced in usual large-scale polygon experiments.

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.

A method is proposed for calculating the mean velocity of the front of a plane detonation wave in a poorly mixed mixture of a gaseous hydrocarbon fuel and an oxidizer (oxygen or air). It is assumed that the chemical composition of the mixture exhibits periodic fluctuations in the detonation propagation direction, e.g., owing to gas charge stratification. The method is based on analyzing the functional dependence of the ideal (Chapman-Jouguet) detonation velocity on the molar fraction (normalized molar concentration) of the fuel. It is demonstrated that the mean detonation velocity can be appreciably (by 10-15%) smaller than the ideal detonation velocity. A dependence is found, which allows one to estimate the degree of mixing of the gas mixture on the basis of mean detonation velocity measurements.

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.

Computer modeling is used within the framework of the theory of density functional to determine the physical and chemical properties of a set of energy materials, which correlate with detonation parameters and sensitivity factors. There are two models of prediction of detonation parameters and sensitivity factors formulated for molecules and explosive crystals that satisfactorily correlate with the experimental data.

The formation of a deposit from mixture of PETN with fine-dispersed aluminum under the action of neodymium laser radiation in a free generation mode is studied. This paper also describes the efficiency of a deposit as a means to reduce the energy of laser initiation of mixtures as a function of PETN dispersion, aluminum content in the initiated mixtures and the deposit, mixture density, and diameter of the region of laser action on the explosive. The compositions of the mixtures for preparation of deposits optimal in composition, which reduce the initiation energy of the mixtures of PETN with aluminum up to 3.75 times, are determined. The mechanism of functioning of the deposit during laser initiation of the mixtures of PETN and aluminum is discussed.

Dependences of the brightness temperature of the detonation front and detonation products on detonation pressure were determined by the pyrometric method in the range of 0.7-9.4 GPa. The pressure was varied by changing the initial density of the emulsion explosive in the range 0.43-1.2 g/cm3. Polymer microballoons were used as sensitizer. The dependence of the brightness temperature in the Chapman-Jouguet plane on detonation pressure is found to be nonmonotonic. In the investigated pressure range, the measured temperature values changed from 2250 to 1830 K. A comparative analysis of the application of polymer and glass microballoons as sensitizers is performed. The obtained experimental data are compared with the calculation available in the literature.

This paper presents the results of investigation of the detonation velocity of an emulsion explosive (HE) sensitized with Expancel polymer microballoons in a wide range of initial density of 0.14-1.33 g/cm3. It is shown that when the density of the emulsion explosive is less than 0.4 g/cm3, detonation with an unstable front characteristic of liquid explosives is possible.