Home – Home – Jornals – Combustion, Explosion and Shock Waves 2024 number 6

It is shown that the wave of flameless spotty combustion of ballasted RDX can propagate in a stable manner in a granulated initial mixture. Under certain conditions, flameless combustion of RDX-containing granulated mixtures can proceed in a vibrational or gushing mode. Based on the process of flameless RDX combustion, a method of single-stage synthesis of high-porosity granules containing nano-sized cobalt or iron particles is developed. The synthesized granulated composite material reveals a comparable catalytic activity in hydrocarbon synthesis by the Fischer-Tropsch method. This material differs from the existing analogs by the absence of pyrophoric properties.

Experiments are conducted to study the instability of detonation waves in mixtures of nitromethane, tetranitromethane, and FIFO with inert diluents by recording the detonation front glow with a NANOGATE-22/16 high-speed eight-channel sixteen-frame electron-optical camera. In the detonation instability region, the detonation front exhibits a nonuniform glow, which is associated with a turbulent flow in the reaction region. The formation of cellular structures with the reaction of the explosive in oblique and transverse waves is not observed in the compositions studied.

This paper presents the results of experimental and computational studies of the influence of a number of factors on the detonation velocity of model mixed explosive compositions: type of explosive and polymer binder, content and particle size of components (explosives, aluminum powder, oxidizer), and charge diameter. It has been found that the detonation velocities of the explosive okfol and mixed compositions based on an active binder with an explosive content of 60-80 % (CL-20, HMX) are close to each other. The most marked decrease in detonation velocity is observed for mixed compositions with a mass content of aluminum higher than 20% with increasing oxidizer concentration from 6 to 30%. An increase in the particle size of the explosive and oxidizer leads to an increase in the experimental detonation velocity of the explosive composition. The critical detonation diameter of mixed compositions based on the active binder is 40-80 mm depending on the content of components.

A simple method of predictive estimation of the yield of detonation nanodiamonds is described, which takes into account the mass fractions of elements in the carbon-containing explosive with a general formula C_aH_bN_cO_d . An empirical dependence of the content of detonation nanodiamonds in the semi-product of nanodiamond synthesis (diamond charge mixture) on the fraction of carbon in molecules of explosives is derived. The yield of detonation nanodiamonds is presented as a function of the fractions of chemical elements in the initial system, which makes it possible to give quantitative predictions of the yield of detonation nanodiamonds.

Results of experimental investigations of the polymorphic transformation β → δ of various fractions of HMX are reported; the studies are performed by methods of differential thermal and thermogravimetric analysis, as well as by picnometer tests. With an increase in the crystal size, it is found that the temperature of the beginning of the polymorphic transformation of HMX decreases, and the HMX density also decreases. It is hypothesized that the change in the polymorphic transformation temperature is associated with the dependence of the enthalpy jump on the polymorphic transformation on structural defects.

The model of a source of shock-induced ejection based on the Richtmyer-Meshkov instability physics and developed for calculating the ejected mass of metal particles and its velocity distribution in the flow is applied to calculate the particle size distribution. The model is developed form metals transforming to a liquid state after the shock wave impact. It is shown that one has to know not only the density and surface tension of the liquid medium, but also the initial amplitude and wavelength of disturbances, as well as the shock wave profile for predicting the particle size spectrum in the case of liquid medium ejection. According to the theory developed, the particle size in the flow is largely determined by the disturbance wavelength than by the initial amplitude. The results are compared with experimental data on the size of nanoparticles ejected from narrow bands with initial disturbances on the free surface on tin and lead samples.

When studying the process of shock-induced dusting, especially when particle fluxes move in a gas or are caused by several shock waves, it is necessary to obtain experimental data on the time history of density in these fluxes starting from the arrival of the shock wave at the free surface of the sample. In this work, such measurements were performed using high-speed radiography with synchrotron radiation. In the experiments, one or two successive shock waves with a pressure of ≈40 GPa arrived at the free surface of tin samples with a roughness Rz 5, 20 and 60. Shock-wave unloading occurred in vacuum or gas (air, helium, nitrogen) at initial pressures 1-8 atm. The paper presents the experimental setups and experimental data on the density dynamics in dust fluxes formed upon exposure to one and two successive shock waves after their arrival at the free surface of samples in vacuum and gas media.

A scheme of registration of displacements of reflecting surfaces by the method of laser ranging with the use of a device developed for measuring the delay of optical signal propagation is considered. Results of test experiments aimed at studying the dusting parameters and spallation fracture of metals under shock wave loading with simultaneous applications of photonic Doppler velocimetry and laser ranging methods are reported.

An approach is proposed that allows for the construction of shock adiabats of molecular crystals of nitro compounds based on data on their isothermal compression. Equations of state for PETN and TATB crystals are constructed for this purpose. The comparative analysis of experimental data on shock-wave compression of a simple PETN crystal and computational results is performed using the proposed approach to converting isothermal compression pressures to a shock adiabat and the constructed equation of state for PETN, presented in the work. As shown by the analysis, the experimental and calculated pressures lie within the limits of experimental error.

This paper presents a semi-empirical multiphase equation of state (EOS) of copper for two solid FCC and BCC phases, as well as a liquid phase with account for vaporization is presented. A wide range of experimental and theoretical data is used to parameterize the EOS. In the field of plasma states of matter, calculations are performed using the RESEOS average atom model and are also applied to develop the EOS. Curves are plotted for FCC-BCC phase transition, for melting, and for liquid-vapor transition. In general, the EOS-based calculations are in good agreement with the experimental data and the results of theoretical calculations in a wide range of temperatures and pressures.

This paper presents the results of an experimental study of dusting and dispersion of a lead sample in vacuum after shock-wave loading and isentropic unloading using optoelectronic microscopy and photonic Doppler velocimetry. The dynamics and spectrum of predominantly dispersed particles are studied. Optical visualization is ensured by cutting out an 0.5-mm wide stream from the dispersed cloud using a diaphragm with a slit. The experiments are carried out in a sealed armored chamber. A 1- or 2.5-mm thick sample is loaded with a solid explosive through a metal substrate 1 and 2 mm in thickness. The shock wave intensity varies from about 23 to 38 GPa, and the pressure gradient behind the wave front ranges from 80 to 157 GPa/cm. After the loading, the lead is either in a liquid phase, in a solid phase, or in a mixture of both. It is shown that the particle size distributions of dispersed lead are different at different phase states.

The currently used shaped charges with combined hemisphere-cylinder liners allows obtaining compact steel elements with velocities of about 6 km/s. In this work, the possibility of modifying hemisphere-cylinder liners to expand the velocity range of the resulting compact elements was investigated by numerical simulation within the framework of the two-dimensional axisymmetric problem of solid mechanics. The simulation was carried out for a 100 mm diameter shaped-charge charge with a copper liner. The jet-forming part of the liner had a degressive (decreasing from top to bottom) thickness, a hemispherical or semi-ellipsoidal shape outer surface, and a semi-ellipsoidal or semi-superellipsoidal inner surface. As a result of the calculations, the geometric parameters of combined liners to form compact elements of maximally possible mass with velocities of 5-9.5 km/s were selected. For an element with a velocity of about 9.5 km/s, the mass was about 5 g.

According to Lavrentiev's hydrodynamic theory, the penetration depth of a shaped-charge jet is determined by its total length. However, experience of practical application of shaped charges has shown that the penetration usually ceases before the jet is completely used up. For a reliable description of experimental results, the effective length and the effective (critical) velocity of the shaped-charge jet are introduced to exclude from consideration the closing section of the jet, which various reasons is not involved in penetration. Effective velocity values are introduced into calculation methods as constants for a specific pair of jet and target materials or in the form of an empirical dependence on the focal length. The possibility of separating the jet into effective and ineffective sections based on physically justified reasons without the need to construct empirical dependences is considered.

This paper presents the results of numerical simulation of the operation of rotating shaped charges. The results show the that the velocity of radial expansion of high-speed hollow cylindrical projectiles simulating shaped-charge jet elements has no influence on their penetration depth. Numerical analysis was performed to study the stretching of a rotating stretchable metal cylinder (jet) with a harmonic lateral surface profile. The influence of various parameters, including the angular velocity of the jet, on its continuity in the axial and radial directions was evaluated. A relation for estimating the ultimate elongation coefficient of a rotating shaped-charge jet is proposed. Comparison of calculation results with experimental data shows that they are in satisfactory agreement with each other.

This paper presents the results of a series of studies to determine the dynamic strength characteristics of samples manufactured using selective laser melting technology of 12Kh18N10T steel powders and compares them with the properties of 12Kh18N10T steel obtained by traditional hot rolling under shock-wave loading in a compression pressure range of 3-7 GPa. It is shown that the steel samples manufactured using selective laser melting technology have greater resistance to short-term tension resulting from the interaction of counter-current unloading waves compared to the hot-rolled 12Kh18N10T steel.

Dynamic properties of volume-structured samples with different topology of mesh structures made of AK6 aluminum and synthesized by selective laser melting are considered. Tests are carried out at quasistatic strain rates of 10²÷10³с^-1 by the Kolsky method using a split Hopkinson bar. Strain diagrams are constructed, and the values of the conditional yield strength and tensile strength are determined. The results of measuring the properties of samples with different topology of mesh structures of FCC and BCC types and triply periodic surfaces of minimum energy of the gyroid type. The effect of the geometric characteristics of gyroids (cell size and wall thickness) on the strength properties of the samples is described. It is shown that gyroids have improved characteristics at the same material density. Mesh metal materials obtained by additive technology can be used in engineering to reduce structural mass and destructive high-energy mechanical effects.