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

We investigated the mechanical response of planar auxetic lattice metamaterials with various cell geometries under thermal loading. The dependance of the structures’ deformation behavior on both the geometry and quantity of the unit cells was established. Specifically, the influence of unit cell shape (auxetic and trapezoidal) and connecting element type (straight and arc) on thermal expansion was analyzed. The obtained results can be used for designing metamaterials with tailored thermomechanical response.

The dependence of reconstructed velocity fields on time delays for two cases with different types of tracers in a typical nozzle flow is studied. Cases with water droplets that vary substantially in size and small oil droplets are considered. Increasing the initial interrogation window has been shown to be quite efficient for reconstructing the velocity field in cases of relatively large time delays exceeding the optimal time delay value. It is shown that the loss of information with an increase in time delay is a gradual process.

Viscoelastic properties of elastomer composites were studied depending on the filler type (carbon black, nanodiamonds, graphene, carbon nanotubes). The samples were subjected to cyclic loading with the amplitude and rate of deformation decreasing at each subsequent cycle (plus stops for relaxation). An analysis of dissipative cyclic losses during loading and unloading was carried out, and their share due to softening of the material due to the Mullins effect was also determined.

We discussed mathematical modeling and research of current density and magnetic field strength distributions in single- and multi-frequency coaxial cables during high-frequency electrical energy transmission.

A nonlinear equation is obtained for the dynamics of a hyperelastic rod, the deformation of the material thereof is described by a neo-Hookean potential. The following quasi-harmonic processes are studied: the generation of a longitudinal double-frequency wave, the formation of a wave package with its amplitude envelope having the properties of a soliton.

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.