Bulletin of the Russian Academy of Sciences: Physics最新文献

Active vibration diagnostics is a promising method for assessing the mechanical condition of large-scale structures. The main element of the vibration diagnostic system is the actuator. It is used to generate diagnostic signals in the structure. Previously, the authors developed an actuator based on piezoceramics. Dynamic deformation of piezoceramics is usually described by linear relations, although it is known that at high values of electric field strength it exhibits nonlinear properties. Therefore, a series of experiments was carried out that allowed us to determine the limits of applicability of a conservative linear model of a piezoceramic actuator.

We presented an experimental study of the regularities of multiple localization of plastic deformation under conditions of the Portevin–Le Chatelier effect during compression of “inclined” cylindrical samples made of AMg6 alloy. An analysis of statistical distributions of intervals of plastic flow stress fluctuations was performed. Calorimetric studies of samples with different degrees of deformation were conducted.

The dynamic strength of concretes under different temperature-velocity conditions is analyzed using the incubation time criterion and the thermal fluctuation theory of strength. The model is validated through comparison with experimental data on concrete with basalt and limestone aggregate. It is shown that the characteristic relaxation time of concrete increases within the temperature interval of 20 to 800°C and decreases at temperatures above ~800°C.

The CeF₃:Tb³⁺ (1%), CeF₃, LaF₃:Tb³⁺ (1%), CeF₃:LaF₃:Tb³⁺ (1%), LaF₃:Ce³⁺ (5%), LaF₃:Ce³⁺ (5%):Tb³⁺ (1%) nanoparticles were synthesized via co-precipitation method. Nanoparticles of mononuclear and core-shell structures had diameters of 70 and 200 nm, respectively, and a hexagonal phase. Spectral characterization of the samples was carried out in the temperature range of 80–430 K with excitation at a wavelength of 266 nm. The luminescence band intensities of Ce³⁺ and Tb³⁺ cerium ions were also calculated as a function of temperature for all samples. It was shown that the structures with spatially separated Ce³⁺ and Tb³⁺ ions have the highest temperature sensitivity: CeF₃:LaF₃:Tb³⁺ (1%) core-shell and a mechanical mixture of CeF₃ and LaF₃:Tb³⁺ (1%) powders. Due to the spatial separation of Ce³⁺ and Tb³⁺ ions and the exclusion of resonant energy transfer between them, it was concluded that for the studied nanoparticles, the main contribution to the temperature sensitivity is the different dependence of the luminescence intensity of Ce³⁺ ions on temperature compared to the similar dependence of Tb³⁺ ions, which makes it possible to measure the temperature based on the ratio of the integral intensities of Ce³⁺ and Tb³⁺.

An array of one-dimensional nanostructures of CdTe solid solution with a hexagonal wurtzite structure in a polymer matrix was obtained for the first time at PET membranes. The electrochemical growth of the nanostructures was carried out using an electrolyte containing CdSO₄ and TeO₂ in a galvanostatic mode at an electrolyte pH of 1.0 using a graphite anode. At a deposition current density of 8.5 A/dm², the formation of a homogeneous array of one-dimensional nanostructures of the CdTe is observed. The obtained arrays of nanostructures are characterized using Raman spectroscopy, X-ray phase analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The characterization results confirm the formation of an array of CdTe solid solution nanowires.

The concentration dependences of the kinematic viscosity and supercooling of Al–Mg melts in the Mg-rich region and Al–Zn melts in the Zn-rich region were experimentally obtained. The extrema found on the viscosity isotherms of the melts under study are consistent with the features on the concentration dependences of their supercooling. The possibility of using the Al₇Zn₉₃ alloy as a solder for the AMg6 alloy was demonstrated.

Nickel ferrite powders with a particle size of 4 nm were prepared by chemical coprecipitation. The imaginary part (chi {kern 1pt}^{{''}}) of the magnetic susceptibility was measured at room temperature with a broadband ferromagnetic resonance spectrometer in the frequency range from 100 MHz to 10 GHz. The obtained frequency dependences of (chi^{{''}}) are described within the framework of an isotropic superparamagnet model taking into account interparticle interactions.

Finite element modeling was performed to simulate the magnetic flux distribution in an H-shaped primary transducer of a magnetic structuroscope for the nondestructive assessment of residual austenite content in VNS-5 structural steel. The dependence of the magnetic induction in the center of the crossbar in the H-shaped magnetic core of the transducer on the difference in residual austenite content between samples was established. This dependence can be utilized for calibrating flaw detectors.

The authors consider using a high-frequency electromagnetic field for the induction heating and heat treatment of parts with coatings resistant to metal corrosion, in order to improve their mechanical properties in different modes of cooling when an induction unit with a developed high-frequency power semiconductor generator is used.

Linear structures ordered into bands were found when studying the morphology of the surface of carbon films consisting of arrays of multiwalled nanotubes. Their geometric parameters were measured, and it was shown that they reflect “frozen” fluctuations in the density of the sputtered material flow, which depend on the mode of operation of the sputtering unit.