This work is devoted to the study of the processes that take place in the welding gap during explosive welding (EW). In the welding gap, when plates collide, a shock-compressed gas (SCG) region is formed, which moves at supersonic speed and has a high temperature that can affect the quality of the weld joint. Therefore, this work focuses on a detailed study of the parameters of the SCG. A complex method of determining the SCG parameters included: determination of the detonation velocity using electrical contact probes, ceramic probes, and an oscilloscope; calculation of the SCG parameters; high-speed photography of the SCG region; measurement of the SCG temperature using optical pyrometry. As a result, it was found that the head front of the SCG region moved ahead of the collision point at a velocity of 3000 ± 100 m/s, while the collision point moved with a velocity of 2500 m/s. The calculation of the SCG temperature showed that the gas was heated up to 2832 K by the shock compression, while the measured temperature was in the range of 4100–4400 K. This is presumably due to the fact that small metal particles that broke off from the welded surfaces transferred their heat to the SCG region. Thus, the results of this study can be used to optimize the EW parameters and improve the weld joint quality.

Проведены эксперименты по исследованию неустойчивости детонационных волн в смесях нитрометана, тетранитрометана и ФИФО с инертными разбавителями посредством регистрации свечения детонационного фронта скоростной восьмиканальной шестнадцатикадровой электронно-оптической камерой НАНОГЕЙТ-22/16. В области неустойчивости детонации зарегистрировано неоднородное свечение детонационного фронта, которое связывается с турбулентным течением в зоне реакции. Формирование ячеистых структур с реакцией взрывчатого вещества в косых и поперечных волнах в исследованных составах не наблюдалось. 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.

Experiments are performed for studying the process of shock wave initiation of detonation in pure tetranitromethane and its mixtures with acetone, nitrobenzene, and methanol. The glowing of the detonation front is detected using streak cameras and frame-by-frame photography. It is found that detonation both in pure tetranitromethane and in its mixtures with dilutants is initiated at localized sites. The number of these sites, the character of their formation, and the features of their growth and merging depend on the nature of dilutants. The evolution of the wave profiles is registered by a multipoint velocity interferometer system for any reflector (VISAR). The resultant velocity profiles are noticeably different from those predicted by the classical pattern of detonation initiation and evolution under a shock wave action.

In the case of multipoint initiation of the side surface of a cylindrical charge in a section perpendicular to the axis, a detonation wave with a complex gas-dynamic structure is formed, which has the shape of a polygon with vertices at wave conjugation points. The sides of the polygon are always convex toward the charge axis. It is stated that a smooth cylindrical detonation wave with reverse curvature can be obtained by using special devices at initiation points: lenses made of an inert material. The dynamic characteristics of the material are experimentally determined, and the method for constructing the lens profile is substantiated. The operation of an initiation node and the formation of a cylindrical detonation wave in a charge are mathematically modeled. The specific features of the operation of a single initiating node and a node that is part of the experimental assembly are shown. The dynamics of axisymmetric compression by a converging detonation wave is presented and compared with calculations.

The results of experimental investigations of the formation of detonation waves with multipoint initiation for the case of a planar and converging cylindrical wave are presented. A special initiation system was used, where the main element was modeled for manufacturing on a three dimensional printer. A solution was found to form a smooth detonation wave for the planar case. Studies of a converging cylindrical detonation wave have shown the need to solve some fundamental issues related to the nonstationarity of such a wave.

An uncomplicated explosive technique, in which a detonation wave is formed using a multipoint initiation, has interesting features. One of them is a complex cellular structure, which consists of nodes and cords. The reasons of these features and ways of their elimination are discussed in the work. The study was carried out using a high-speed camera with nanosecond resolution. Methods for smoothing a detonation wave formed with multi-point initiation are presented.

The results of the experimental investigations of the dynamics of the axisymmetric compression of a metallic liner are presented in this work. The studies were carried out using a high-speed camera with nanosecond resolution. It is shown that the detonation wave formed by the multipoint initiation method has a complex three-dimensional cellular structure, where first-order node lines and second-order nodes are present. The hydrodynamic instabilities formed upon the exit of the shock wave onto the inner surface of a metallic liner do not smooth out as they contract, but increase.

One method of studying materials or plasma under pressure pulse loading is axisymmetric compression using a convergent cylindrical detonation wave. Such waves are often generated by multipoint initiation and have a number of specific features that may affect the properties of the test objects. To solve specific problems, it is proposed to use a laboratory explosive system based on a converging cylindrical detonation wave with 12–48 initiation points. The TNT equivalent of the charge is less than 1 kg. The main method of research is visualization using a domestic high-speed Nanogeit camera with a nanosecond time resolution. The structure of the converging detonation wave is shown, and its velocity along the radius is determined. It is shown that for a charge of limited thickness, the curvature of the detonation wave front for various explosives depends only on the distance to the initiation point.

The results of investigation of the detonation waves structure, the critical diameter, detonation parameters and the dependence of detonation velocity on the charge diameter for pressed hydrazine nitrate (HN) charges in the density range of 1.40–1.68 g/cm3 are presented. It was found that the critical diameter drops with the initial density decrease. Under steady-state detonation conditions at an initial density of 1.68 g/cm3, a high detonation velocity of 8.92 km/s is observed in HN charges. The change of the detonation velocity with variation of the initial density is not monotonous, but has a characteristic s-shape.

The experimental results showing the formation features of a cylindrical detonation wave with a multipoint initiation are presented in this work. One of the main features of the process is the presence of the "nodes" on the detonation wave, i.e. points of convergence of detonation waves from the neighbor points of initiation. The other feature is the presence of the "bundles" which are exeunt to the detonation products. Nodes are the points with high energy level at detonation front. They may cause hydrodynamic instabilities during the compression of a metal liner. Parietal flows in the cell structure of detonation products may be reason for formation of "bundles". It should be noted that the detonation wave is always convex between the neighbor "nodes", although in the initial moment the triple-wave Mach configuration is forming and it should lead to aligning of cylindrical wave. The experiments with the use of high explosives with different densities (from 0.95 to 1.65 g/cm(3)) were carried out on the laboratory installation. The characteristic features of the detonation wave formed by the multipoint initiation can be seen both in solid and in liquid high explosives. Different design features (interlayers made of different materials etc.) did not lead to disappearing of "bundles" and smoothing of "nodes" at the detonation wave.

Experimental investigation of unstable detonation front structure in mixtures of liquid high explosives (nitromethane and FEFO—bis-(2-fluor-2.2-dinitroethyl)-formal) with inert diluents (acetone, methanol, DETA—diethylene triamine) has been carried out. Inhomogeneities have been registered by electro-optical camera NANOGATE 4BP allowing to make 4 frames with the exposure time 10 ns. According to experimental results the detonation front in nitromethane–acetone mixture is unstable. It is evident that pulsations on detonation front do not form spatial periodic structure and their dimensions differ several times. But mean longitudinal size of pulsation is about 500 μm at 20 wt% of acetone concentration. This means that the typical size of cell equals to reaction zone width. The same structure of cellular front have been registered in 70/30 FEFO–methanol mixture. Second kind of instability, failure waves, was observed in neat nitromethane at the free surface. In this case the stability loss result in turbulent flow which is clearly detected in the shots obtained. Adding small amount of DETA (0.5 wt%) results in disappearance of the failure waves and flow stabilization. The effect is caused by the fact that DETA sharply accelerates initial rate of chemical reaction because it is sensitizer for nitromethane.

One of the methods of experimental investigation of cylindrical detonation wave formed by the multipoint initiation method is presented in this work. The experimental setup was specially developed for this purpose. Two types of "Nanogate" high-speed cameras were used in the experiments. The phenomenological descriptions of initiation process, dynamic of formation of detonation wave and gas dynamic flow of detonation products are presented. This method in combination with the other modern methods will allow carrying out more profound investigations of such problems.

The behavior of docosane (C22H46) and cerium (Ce) under shock-wave action has been investigated. It was shown that the solid docosane demonstrate elastic-plastic properties and has abnormal compressibility at pressures below 100 MPa. It was found that the strength of docosane remains practically constant and equals to about 24 MPa when passing through the melting point. We determined the shear stress and evolution of compression wave in the area of cerium anomalous compressibility. The value of longitudinal stress at which the γ-α phase transition occurs is also determined. It is shown that the phase transition pressure, under dynamic and static compression coincides and is equal to 0.8 GPa. The spall strength of cerium rises from 0.3 to 0.7 GPa when strain rate increase from 2.1 x 104 to 1.02 x 106 s-1.

The structure of the compression pulse in and the spall strength of paraffin and docosane are experimentally studied. It is found that the strength of paraffin decreases by a factor of 1.5 when the melting temperature is passed (from 20 to 14 MPa), and the strength of docosane remains almost unchanged (about 24 MPa). Docosane in the solid state is shown to exhibit elastoplastic properties and to have anomalous compressibility at a pressure below 100 MPa. The possibility of application of a homogeneous nucleation model to interpreting the obtained data is discussed.