Journal of Applied Mechanics and Technical Physics最新文献

We present the results of an investigation on the erosive wear of polycrystalline diamond coatings grown on molybdenum substrates. Prior to diamond deposition, the molybdenum substrate surface was treated with a flow of alundum or silicon carbide microparticles. Diamond coatings were grown on the substrates via gas-jet deposition from a H₂–CH₄–Ar mixture activated in a microwave discharge. Substrate surface pretreatment has been shown to ensure an increase in the wear resistance of the diamond coatings.

This research investigates the influence of Nb₂O₅ coatings, produced by using reactive sputtering technique, on the surface of middle-tension specimens M(T), regarding fatigue crack growth curves (da/dN versus ΔK) under exposure to a 0.6 mol L^–1 NaCl saline solution. Results demonstrated the corrosion process occurred in the vicinity of the crack tip, where stresses are elevated, and significant plastic deformation prevails, notably influenced by slip bands that induce microcracks, exposing fresh material layers to the corrosive surroundings. The Nb₂O₅ coatings enhanced the fatigue-corrosion resistance of the 2198-T851 aluminium alloy. This study marks an initial step towards more comprehensive investigations into the impact of Nb₂O₅ coating on improving the mechanical properties of the 2198-T851 aluminium alloy.

The paper presents the results of numerical simulation of the electrophoresis of a single spherical ion-selective granule in a viscoelastic electrolyte within the Oldroyd-B and FENE-CR fluid models. The study is limited to weak and moderate electric fields, which corresponds to electrophoresis of the first kind. The dependence of the granule’s electrophoretic velocity on the polymer concentration and relaxation time is obtained.

For 30KhGSA grade steel with different hardness, two methods of creating a weld by explosive welding of low-plastic materials without cracking have been experimentally investigated: 1) the use of welding modes that lead to the formation of a flat, waveless contact zone; 2) the use of a ductile intermediate layer, so that the welding modes corresponding to the strength properties of the material of this layer can be applyed. A scale of characteristic sizes has been constructed that marks the bounderies between the flow zones of the material with different strain rates and makes it possible to estimate the thickness of the plastic deformation localization band and the zone of intense plastic deformation. It is shown that the minimum thickness of the intermediate layer, at which it is not fragmented during joint plastic deformation of the welded plates, is determined by the thickness of the plastic deformation localization band. The principal possibility of explosive welding of plates with an intermediate layer produced by detonation spraying is shown for the first time.

An approach is presented for estimating the average acoustic velocity in the annulus of a mechanized well, which is subsequently used to determine the gas–liquid interface (dynamic level). This approach accounts for the distribution and variation of gas component analysis, thermobaric conditions, and the presence of phase transitions. The main step in solving the problem is to determine the gas composition distribution in the region from the wellhead to the gas–liquid interface. The approach is based on the laws of thermodynamics of equilibrium processes. The approach is tested in more than 100 wells at several fields in Western Siberia. The convergence of the testing results is verified by comparing them with field experimental measurements of acoustic velocity via acoustic well sounding.

The study investigates the possibility of controlling the structural and phase state of the titanium matrix composite Ti–6Al–4V–B₄C during direct laser deposition. A correlation has been established between the laser processing modes and the microstructure of the composite: variations in energy parameters lead to changes in the concentration of secondary phases (TiB, TiB₂, TiC). In this work, synchrotron radiation was utilized for phase analysis, allowing for the determination of the phase composition of the composite through diffraction patterns. It was demonstrated that increasing the laser energy input affects the microhardness of the material, resulting in a 25% increase. The study also evaluates the efficacy of employing additional substrate heating to regulate the extent of dissolution of the initial ceramic particles within the metallic matrix by varying the laser radiation modes. Phase transformation analysis in the titanium matrix composite was performed using X-ray phase analysis with a synchrotron radiation source.

The frequency spectrum and modes of bending vibrations of rectangular plates in contact with a liquid or gas are determined. An expression is obtained for the distributed transverse load on a plate hinged along the contour. The surfaces of the plate are in contact with a medium of different density and pressure. The medium can be both compressible and incompressible. The effects of the average pressure, the curvature of the middle surface, and the added mass of the gas medium on the bending are determined.

This paper presents an overdeterministic algorithm for constructing the asymptotics of the stress field near the tip of a nanocrack in an anisotropic linear elastic body with cubic symmetry. A molecular dynamics solution of the problem of mixed loading (mode I fracture and transverse shear) of single-crystal copper and aluminum nanoplates with a central cut is described. Based on this solution, an asymptotic representation for the stress tensor components was derived. The atomistic stresses in the vicinity of the crack tip were calculated, and the coefficients of the series representing the stress field were determined using the values of the atomistic stress tensor components. The molecular dynamics calculations were performed for a temperature of 10 K to exclude the occurrence of nonlinear elastic deformation near the crack tip. The stress fields in the atomistic and analytical solutions were compared. The stresses at different distances from the nanocrack tip are in good agreement with the solutions of problems of classical macroscopic theory of anisotropic elasticity and can be described using a series that extends the Williams series to anisotropic media. In the series extended to anisotropic materials, the regular (nonsingular) terms are taken into account and the series coefficients of these terms are determined. It is shown that the developed algorithm can be used to effectively determine the coefficients of the higher-order terms of the series.

Erosion of electrodes in a three-electrode pulsed X-ray tube with a rechargeable insulated electrode operating in the explosive emission mode at a voltage of 600 kV and pulsed current up to 1000 A was investigated. Erosion was produced by the action of high pulsed electric fields and pulsed flows of electrons and plasma during vacuum breakdown in X-ray tubes. X-ray fluorescence microanalysis using a scanning microscope revealed the presence of numerous metal balls of size 10–40 (mu )m formed from both the tungsten anode material and the material of the third insulated Kovar electrode. Several stages of detachment of the balls by the electric field were detected on the insulated electrode. The critical values of the Coulomb forces at which droplets arise in accordance with a dynamic model (taking into account the kinetic energy accumulated by the mass during the time of exposure to the electric field and surface energy) and the electric field pressures during the operation of the tube were estimated, allowing an explanation of the observed phenomena.

In this paper, we have approximated the solutions of the Cahn–Hilliard equation (CH) with the logarithmic potential function which arises in the modeling of phase separation of binary alloys. The CH equation is a high-order nonlinear equation, consequently, utilizing a common difference scheme on the CH equation causes long stencil schemes. To resolve the faults of long stencil schemes, we split the CH equation to second-order system under the Neumann boundary condition and we applied second-order scheme based on the 2D Crank–Nicolson method to discrete it. The uniqueness and error estimation of the approximated solution is proved. Also, preserving the conservation of mass and decreasing the total energy are investigated. Finally, to confirm the theoretical results, three examples with various initial conditions are presented.