Vol 516, No 1 (2024)

The authors provide the performance and experiment results of the isentropic compression of the tungsten VNM-3-2 alloy up to ultra-high (>1 Mbar) pressures in a device based on the magneto-cumulative generator. The points obtained on the diagram “compression-pressure” are compared with a normal isentrope constructed based on the data of shock-wave experiments.

The results of numerical calculations of the destruction of the protective shields of the spacecraft under the action of a micrometeorite impact are presented. A gas-dynamic numerical simulation of the process of high-speed penetration by micrometeorite of a spaced protective shield of a spacecraft has been carried out, taking into account fragmentation and the formation of a cloud of fragments after passing through the protective shield. In a three-dimensional formulation, the calculated configurations of the cloud of fragments of the impactor and the target for the initial velocities of the impactor up to 10 km/s are obtained. The high efficiency of the used design of a protective screen made of multidirectional corrugated grids as a means of fragmentation and dispersion of the kinetic energy of impact of small high-speed particles, reducing the average pressure pulse on the protected device by two to three orders of magnitude, is shown.

The article research the microstructure of the welded layer obtained by exposure to an ultrashort laser pulse on a glass-metal joint. The study of the weld made it possible to identify the effect of thermal diffusion of the chemical elements of glass and metal into the joint zone in a ratio of 50 : 50% of each material. The size of the transition layer of the welded joint between glass and metal was 2–3 microns. The results of the work also show that when combining chromium-nickel stainless steel with borosilicate glass, bonds of the Fe–O–Si type are formed, and the connection of a 6000 series aluminum alloy with borosilicate glass leads to the formation of aluminum oxides Al₂O₃.

In connection with the promising use of sandwich shells in the designs of modern technology and primarily in aircraft, the methodology of building models for studying the aeroelastic stability of sandwich shells reinforced with annular ribs and an internal hollow cylinder is considered. Equations are obtained and the main stages of solving the problem using the proposed set of methods are considered. Dependencies were constructed with the help of which the influence of the thickness of the reinforcing cylinder, the number of annular ribs and the length of the shell on the critical speed of flow was studied. The considered methodology makes it possible to construct an initial approximation model for studying the aeroelastic stability of reinforced sandwich shells.

We study the nonlinear dynamics of a rectangular atomically thin nanostrip under conditions of internal combinational resonance between two transverse and one longitudinal modes of mechanical vibrations. Conditions have been analytically found for the initial pretension of the layer required to realize resonance between eigenforms with given indices of variability along the length. It is shown that under conditions of internal resonance, a nonlinear mode of free oscillations is excited in the system, the spectrum of which has the form of a frequency comb. Two qualitatively different types of oscillations of this kind are identified – those caused by the initial excitation in the working longitudinal form of oscillations and in two transverse forms. A significant dependence of the spectral composition of the generated frequency combs on the relationships between the amplitudes of the initial disturbance for the three interacting modes and on the value of the internal frequency detuning parameter of the system is shown.

In this paper, a conclusion about the self-similar behavior of the bed surface evolution is made. It is based on the analysis of experimental and numerical studies of the bed surface evolution under the mechanical impact of liquid flow. The bottom wave has a form close to one period of a sinusoidal function with a time-varying wavelength and constant steepness. A method of constructing the automodel dependence of the bed surface on time and spatial coordinate in analytical form is proposed. It was shown that it is enough to select five bottom surfaces with given wavelengths from a series of shapes. Next, the mean values of shear stresses are calculated for them, and the rates of change of wavelengths are found. Then a degree of approximation of the wavelength dependence of its rate of change is determined, and, finally, the exact solution of the corresponding differential equation is obtained. Comparison with experimental data and numerical solutions shows that the solution error does not exceed a few percent and that computational time is reduced by 25–30 times.

Designs of optical bandpass filters have been developed on planar structures, which were obtained by vacuum deposition onto quartz glass (SiO₂) substrates of three layers also of quartz, which are half-wavelength resonators separated from each other, from free space, and from the substrate by four layers of silver (Ag). The thicknesses of the Ag and SiO₂ layers were determined based on the given parameters of the filter passband by parametric synthesis of one-dimensional models using electrodynamic analysis. In this case, experimental frequency dependences of the real and imaginary parts of the permittivity of silver were used. The measured frequency responses of the manufactured prototypes of red, green and purple filters are in good agreement with the responses obtained during synthesis.

The problem of energy release in hierarchically structured media that are “pieces” of matter of various sizes, contained large quantity of reacting particles, for example, molecules, is investigated. The extremes media here are single–molecular (non-clustered) gases of these substances on the one hand, and homogeneous condensed substances on the other. Under natural assumptions about the different quantity of a substance that can enter into an energy release reaction (combustion, explosion, etc.) due to their location on the surface / inside the structure, the dynamics of access to reacting molecules and the obvious probabilistic nature of the process, a combinatorial procedure is carried out to determine the most probable distribution of energy release. In some simple approximation, the energy release is determined by a single parameter of the combinatorial scheme. The most probable distribution is coincided with the distribution of the unconditionally minimum values of energy release. The result may be used for quantitative interpretation of the difference in the values of the heat of combustion, explosion and other processes under various conditions.