Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2025 number 1

This paper presents the results of mechanical tests of explosive samples. Strain diagrams and the dependence of Poisson's ratio on strain at a temperature of 20, 60, 80, 100 °C were obtained. Curves of the mechanical characteristics of the explosive versus temperature were plotted. The rigidity, strength, and deformability of the explosive were shown to decrease with increasing temperature.

To develop a technology of fracturing a drill pipe with its subsequent extraction from a well at a depth of more than 5000 m, we performed a numerical study of the shock-wave loading of the inner surface of the pipe by the detonation of a special cylindrical charge. Two cases of detonation of the cylindrical charge explosive are considered: plane front detonation and diverging spherical detonation. The computational model is a layered structure which consists of a cylindrical explosive charge in a copper casing, a steel pipe, and drilling mud. The shock-wave impact on the drill pipe is calculated in a three-dimensional formulation using the Eulerian multi-component approach. The calculations confirmed the possibility of fracturing the drill pipe in the region of the lock joint. It is shown that shock-wave impact by plane front detonation far exceeds in pipe damage the impact by diverging spherical detonation. The minimum charge length sufficient for fracturing the drill pipe was determined from the results of additional calculations.

Arrhenius activation energy, zero nanoparticles flux, and internal heat generation effects on natural convection about an isothermal cylinder of elliptic cross section filled with a nanofluid are numerically analyzed in this paper. The nanofluid model involves Brownian motion and thermophoresis effects. The boundary condition of the zero nanoparticle flux causes the results to be more realistic and useful. By using a suitable coordinate transformation, the non-similar governing equations are achieved and then solved by Keller box method. Performing the comparisons with previously published work obtains the good agreement. The dimensionless temperature profiles and the Nusselt number results for the main parameters are presented in graphical and tabular forms. The physical aspects of the problem are discussed in details.

A mathematical model of filtration of solutions has been formulated taking into account the osmotic effect that occurs in porous media containing semipermeable inclusions. A solution of the nonlinear problem of osmotic convection was obtained based on the model using the Galerkin method. The properties and characteristics of convection caused by osmosis have been studied.

An experimental study is performed on the influence of surface slots (grooves) with a depth of 0.18 mm (the depth-based Reynolds number is Re_h = 1000) with orientation angles φ = 0, 30, 45, and 90° on the stability of a supersonic boundary layer on a flat plate. Experiments with natural disturbances at the free-stream Mach number M = 2 are performed. It is found that the maximum rates of the spatial growth of disturbances decrease as the slot orientation angle decreases from φ = 90° to zero. At φ = 0 and 30°, they become smaller than the corresponding values for a smooth plate. The results obtained show that the instability of the first mode of the supersonic boundary layer, which determines the laminar-turbulent transition at M = 2, can be stabilized by small-depth slots with moderate angles of their orientation (0° ≤ φ < 40°).

This paper presents the results of an experimental study of the flow structure in a semi-cylindrical groove located on one of the walls of a rectangular channel with a height H = 0.02 m and a length-to-width ratio of 7.5. A groove with a width D = 0.0158 m and a length L / D = 6.65 calibers could be located at different angles to the longitudinal axis of the channel (φ  = 0÷90°). In the experiments, we measured the pressure in median sections along and across the trench and the velocity components and their pulsations in the longitudinal and transverse directions. In the experiments, the Reynolds number calculated from the average flow rate velocity and the hydraulic diameter of the channel was constant and equal to Re_ch = 3.88 • 10⁴. The pressure distribution on the trench wall in both the transverse direction and along its length was found to depend significantly on the angle of its rotation relative to the channel axis. At the inlet section of the trench, where the flow enters, a zone of strong rarefaction is formed. The length of this zone along the trench does not exceed one caliber, and outside this zone, the pressure coefficient remains practically unchanged up to the outlet of the trench, where there is a sharp increase in pressure due to deceleration. The greatest rarefaction in the transverse direction relative to the trench is achieved at an inclination angle of φ = 45°. The flow structure in different sections along the trench length was studied. The maximum velocity of the circulation flow in the semi-cylindrical trench was obtained at its inlet. As the flow moves along the trench, the intensity of the vortex flow of the gas significantly reduces, and in the case of small trenches ( Δ / D = 0.22), the flow becomes continuous.

The occurrence of longitudinal and transverse vortices in a subsonic air jet and in an air jet with added helium due to the natural instability of the flow is shown using a high-resolution direct shadow method.

A numerical finite-volume method of solving averaged Navier-Stokes equations closed by a one-parameter Spalart-Allmaras turbulence model is discussed. The proposed method is implemented within the framework of the HyCFS numerical code and is verified through comparisons of the HyCFS numerical solutions with those predicted by the CFL3D and FUN3D numerical codes. Three test cases are considered: flow past a flat plate, flow past a flat plate with a roughness element, and flow in a cocurrent jet. It is shown that the numerical solutions obtained are in good agreement with each other. The numerical data on the flow velocity in the mixing layer are compared with experimental results.

Thermophoretic motion of a spherical evaporating droplet in a viscous binary gas medium at arbitrary relative temperature differences in its vicinity is theoretically described in a quasistationary approximation at low Reynolds and Peclet numbers. A system of gas-dynamic equations is solved, including a velocity-linearized system of Navier-Stokes equations, as well as heat and mass transfer equations. The properties of a gaseous medium are described with account for the power-law dependence of the transfer (viscosity, diffusion, thermal conductivity) and density coefficients on temperature. The resulting numerical estimates suggest that the dependences of the thermophoretic force and the velocity of the droplet on the average temperature of its surface are nonlinear.

Kelvin-Voigt equations for inhomogeneous fluids with a singular right side are studied. A singular term that approximates the Dirac delta function on an initially infinitely thin layer is introduced into the right side of a mass balance equation. This singular term is similar to the relaxation term used to describe nonequilibrium processes in hydrodynamics. In an extreme case, when a small parameter, namely the characteristic size of the initial layer, tends to zero, the density and velocity at the initial time change abruptly.

A plane problem that describes the motion of a two-dimensional cavity located in a heavy ideal incompressible fluid is considered. Profiles of the free boundary are constructed by mean of semi-analytical methods, and the motion of virtual singular points of the solution is studied.

A rotationally symmetric flow of an aqueous solution of a polymer in a layer bounded from below by a solid wall rotating with a specified angular velocity around the axis perpendicular to this plane and by a flat free surface from above is considered. The influence of the relaxation viscosity on the solution behaviors and the dependence of the fluid layer thickness on time in various regimes of plane rotation are studied.

The direction of propagation of a straight-line plane crack in structurally inhomogeneous (grainy) materials under the combined effect of loading corresponding to fracture modes I and II is studied. The theoretical curve of the material strength or the Coulomb-Mohr curve type is assumed to be known. Based on the Neuber-Novozhilov force (integral) criterion relations are derived, which allow one to determine the angles of kinking (branching) of the crack trajectory in the case of an arbitrary generalized stress state. Asymptotic presentations of the stress components in the vicinity of the crack tip take into account non-singular terms ( T -stresses). It is found that the crack can develop: 1) normal to the maximum stress direction if there are no shear stresses near the crack tip (Erdogan-Sih hypothesis) in the case of brittle fracture; 2) along the maximum shear direction if there are no normal stresses near the crack tip in the case of viscous fracture (in this case, a dislocation is emitted); 3) along a certain direction corresponding to a mixed stress state in the case of quasi-brittle or quasi-viscous fracture. The crack propagation direction depends on the ratio of the stress intensity factors for fracture modes I and II, sign of T -stresses, and shape of the theoretical curve of strength on the plane of the critical states.

The results of the study of the strength and stability of oval composite cylindrical shells under axial compression are presented. The geometrically nonlinear problem for the shell is solved using the finite element method. The geometric dimensions of the shell are close those of fuselages of modern passenger aircrafts. Another phenomenon described in this paper is the effect of the cross-sectional out-of-roundness of the shell, the nonlinearity of the initial stress-strain state, and the stacking of monolayers by thickness on the critical loads and weight efficiency of composite and metal shells.

A moving edge dislocation in an infinite elastic medium is considered, simulating a stationary shear fault in the Earth's crust at a depth of seismic activity, which increases as quickly as transverse waves travel. Based on the expansion of the vector displacement field into the sum of the potential and solenoidal fields, an exact singular solution to the problem in a plane formulation in the form of convergent series is constructed. An approximate solution in the form of series segments is analyzed in the Matlab computer system using numerical differentiation and integration procedures. The independence of the invariant J-ntegral, whose value is equal to the driving force of the dislocation (the energy spent on the motion of the dislocation by a unit distance), on its velocity is shown.

Solutions to a problem of a solid circular rod made of orthotropic creep material and subjected to torsion by a constant moment are generalized to the case of an annular rod. Calculations are carried out using the Bhatnagar-Gupta method, the method based on the principle of minimum additional scattering, and the finite element method. It is shown that the characteristic parameter method can be used to estimate a stress-strain state. The resulting analytical dependences of the angular velocity of torsion on time at the steady-state stage of creep can be used to determine the shear parameters of the orthotropic Hill potential in torsion experiments or to refine them if these parameters were obtained via other approaches.

This paper presents the theoretical study of how the stress-strain state in a shell mold (SM) is affected by the angle of contact of a support filler (SF) surface with the SM provided that this angle of support can prevent the spherical SM from failure due to temperature stresses within it. The problem of optimization of the resistance of the spherical SM as a function of the angle of contact of its SF while the solidifying spherical casting within it cools down is formulated. The problem is solved using Navier equations, a heat equation, and a numerical method. The numerical scheme and the algorithm developed for solving the problem are given. It is shown that the crack resistance of the ceramic SM is determined by the normal stress value. The resulting resistance of the spherical ceramic SM is analyzed with account for the dependence of the shear modulus of the mold material on the SF temperature.

Molecular dynamics (MD) simulations have been performed to study the uniaxial tensile responses of nano-polycrystalline niobium. Models with different grain sizes were established by using the Voronoi algorithm, and the effects of grain size and system temperature on the mechanical properties of polycrystalline niobium were investigated. The results indicate that grain size has a significant impact on deformation mechanism of nano-polycrystalline niobium. During the deformation process, the number of atoms at grain boundaries rises significantly, while dislocation density gradually decreases. Young’s modulus and yield stress reduced with reduction of grain size, which accords with inverse Hall-Patch formula. Specimens with smaller grain size have more grain boundaries and a larger proportion of chaotic atoms on grain boundaries, which leads to a decrease in mechanical properties. Young’s modulus and yield strength show an inverse relation with increase in system temperature, which is due to the higher temperature enlarge the number of disordered atoms at grain boundaries.