Home – Home – Jornals – Combustion, Explosion and Shock Waves 2018 number 5

For about 15 years, researchers of the Russian Federal Nuclear Center - All-Russian Research Institute of Experimental Physics (RFNC-VNIIEF) have performed studies of fast gas-dynamic processes using a proton radiographic system developed jointly with the Institute of High Energy Physics on the basis of an U-70 accelerator. The main advantages of flash proton radiography over widespread flash X-ray radiography are spatial resolution, multi-frame mode, transmission capability, dynamic range of recording, etc. In recent years, effort has continued to extend the capabilities of the proton radiographic system by increasing the total time and expanding the recording field and equipping it with additional diagnostic techniques and new explosion-proof chambers. In this paper, we present the results of studies that illustrate these capcbilities.

Experiments were performed to study the spherical compression of deuterium and helium to pressures of ≈3000 GPa in a quasi-isentropic regime. The process was recorded by a multi-frame radiographic system which produces up to nine X-ray images of a cavity with gas at various times in one experiment. X-ray images show that explosive devices provide a cavity shape close to spherically symmetric with gas up to the maximum compression of the gas. The experimental data are in good agreement with the results of calculations performed using the RFNC-VNIIEF equations of state of the gases studied. The results of these calculations are used to determine the parameters of the region of compressed gas states reached in the experiments: for deuterium, density 5.5 g/cm³ and pressure 3.6TPa; for helium, density 4.7 g/cm³ and, pressure 2.4 TPa.

This paper describes an experimental study of isentropic compression of a VNM-3-2 heavy tungsten alloy by a pressure of a superstrong pulsed magnetic field, induced by a magnetocumulative MK-1 generator. Experimental points obtained on a p- ρ-diagram of the alloy are compared with its cold compression curve, previously constructed on the basis of shock-wave experiments. The purpose of this study is to correct and clarify a state equation of the alloy under an ultrahigh pressure and low temperature. This equation is used to analyze data obtained in experiments on isentropic compression of various substances.

The structure of bismuth samples after shock-wave loading at pressures of 0.7-2.4 and 22-32 GPa was studied. Before loading, samples were at room temperature or heated to 230-240 ^oC. Loading by a pressure of 1.5-2 GPa at an initial temperature of 233-240 ^oC led to a structural change in bismuth, indicating melting of the sample in a shock wave. The time of shock-wave action was ≈0.7 μs.

Shock wave properties of porous specimens made on the basis of matrices composed of inert and chemically active media (silicon rubber and emulsion, which is an aqueous solution of ammonium nitrate with mineral oil and emulsifier) are studied. The porosity of the specimens is generated by using a filler composed of glass microspheres. The wave velocity profiles are measured by a VISAR laser Doppler interferometer. It is shown that the shock compressibility of porous silicon rubber at pressures below 0.1 GPa displays an anomalous behavior, resulting in smearing of the compression pulse front propagating over the specimen. In the emulsion matrices without microspheres, there are no noticeable chemical transformations up to the pressure of 15 GPa. Addition of microspheres drastically decreases the threshold of chemical reaction initiation and leads to the formation of a steady detonation wave.

Shock compressibility of porous specimens made of mixtures of micro- and nano-sized nickel and aluminum powders is experimentally studied in the pressure range up to 60 GPa. shock wave profiles in the specimens are recorded, and shock adiabats are determined. The equation of state of the specimens is derived within the framework of the Zel'dovich model. The shape of the shock wave profiles does not reveal any specific features that can be associated with a possible reaction between the species. The shock adiabats of the specimens of two types of powder mixtures coincide within the experimental error despite significantly different sizes of powder particles, which implies that either there are no noticeable chemical transformations or, vice versa, they are completed within the shock loading time. The predicted shock adiabat with the reaction between the species being ignored passes in an immediate vicinity of the experimental data, which testifies to the absence of the reaction.

This paper describes experimental results on using nonstationary spectrometry in a terahertz frequency range to determine the composition of gaseous products of decomposition of energy materials. Dependences of analytical signals on lines of the main products of ammonium nitrate and PETN decomposition on time are obtained.

A number of physical and chemical processes occurring under the action of a laser pulse in nanosized aluminum and aluminized explosives on the basis of fine-grained PETN and benzotrifuroxane along with estimates of the effect of aluminum of the dynamics of explosive transformation in these explosives conclude that it is possible to initiate aluminized explosives by laser radiation. The estimated and experimental results show that the main source of hot points capable of causing an explosive transformation in aluminized explosives under the action of a laser pulse can be a compression wave that forms as a result of rapid evaporation of asufficient number of aluminum particles. It is shown experimentally aluminized explosives based on fine-grained RDX and HMX can be initiated by a laser pulse whose source is no more powerful than that in the case of PETN and benzotrifuroxane.

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.

Particles are discharged from surfaces of materials under a shock-wave load. Experimental results on determining the minimal values of a specific weight of particles with which their velocity can be detected using a heterodyne interferometer (PDV method) are presented. An effect of multiple frequency shift of a Doppler signal in the case of laser radiation being reflected from surfaces of materials and a semitransparent layer of dust particles is described.

This paper presents the results of an experimental study of the particle ejection into a low (0.05 atm) vacuum with a narrow (0.2-0.8 mm) rough (Rz = 20-50 μm) surface of the lead sample under the action of a shock wave of intensity about 17 and 34 GPa. The flow was recorded with a video camera in a microscopic mode with a short laser illumination. Due to the small optical thickness of the dust flow, particle spectra approximately 80% of its height measured from the front of the flow were obtained. It was found that when the lead is in the solid state (17 GPa), s jets consisting of a lot of particles are ejected from the rough surface; when the lead is in the liquid state (34 GPa) a lot of thin (from 7 μm) microcumulative jets are ejected from the metal surface, which with time decay into particles.

A heterodyne interferometer is used (PDV method) to study a particle discharge from the free surface of lead samples of different roughness under a shock-wave load. In experiments, the velocity of the free surface of samples and the dust flow velocity are determined, and indicator foils and thin glasses are used to calculate the specific weight of the dust. Dependences of the specific weight of particles on their relative velocity are constructed. The effects of roughness and phase state of the substance after a shock-wave load on the possibilities to determine the velocity of the free surface and the specific weight of discharged particles using indicator foils. It is shown that, with given surface roughness, the specific weight of dust, discharged from the surface during lead melting under the action of a shock wave or load wave, is much larger than in a sample being in a solid state.

This paper described a piezoelectric method for measuring the density and mass of dust flows ejected from the free surface of a condensed material upon arrival of a shock wave at it and its implementation in the Russian Federal Nuclear Center - Institute of Experimental Physics (Sarov). Piezo sensors, methods of recording and signal processing are presented. Results of measurement of the density and mass of dust flows by piezoelectric, radiographic and protonographic methods, and method using indicator foils are compared.

The mass distribution along a flow of microparticles is measured by methods of synchrotron radiation from the VEPP-3 collider. The use of the soft spectrum of radiation allows microparticle flows to be measured with a record-beating (minimum) specific density (1 mg/cm³). Simultaneous recording of microparticle flows by piezo-electric sensors offers a possibility of comparisons and extension of results.

The paper describes a method of simultaneous measurements of kinematic parameters of a fast process by a microwave radio interferometer with a 3-mm range of wavelengths and the brightness temperature of the same process by the microwave radio interferometer operating in the radiometer mode. The methods of radiometer calibration and analysis of radiometric data are described. Results of experimental investigations are reported by an example of measuring the detonation velocity and estimating the brightness temperature of the detonation front in TNT.

A TKPF269 streak camera with mirror scanning and a photosensitive element based on a CMOS matrix were developed for the purpose of replacing film in high-speed cameras with mirror scanning (SFR-2M, USF-2, etc.). A brief description of a TKPF269 streak camera is given. The spatiotemporal picture of the emergence of light radiation from the ends of optical fibers upon firing of an explosive in a model assembly was simultaneously recorded by a TKPF269 streak camera and a USF-2 photo-recording camera to compare the metrological characteristics of these cameras. The results of experimental data processing are presented.

Currently, the computer simulation of the behavior of products containing explosives at various stages of their life cycle has become of increasingly greater importance. Computational methods have been verified by studying the propagation of a detonation wave in channels of model distributors using high-speed photography. This paper focuses on the motion of a detonation wave at the bends of the channel and the formation of dark areas. The results obtained using a NANOGATE 2000 optoelectronic system based on a NANOGATE 22 high-speed camera with a shooting frequency of up to 10⁹ frame/s are presented. The position of a detonation front moving with bends at an angle of 60, 90, and 120^oC was first visualized with an exposure time of 20 ns and an interframe interval of 80 ns.