Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2025 number 5

This paper presents experimentally obtained shadowgraph images of the shock wave structure in an unsteady supersonic reacting flow of a hydrogen-oxygen mixture, generated by a spherical projectile flying at a velocity exceeding the self-sustained detonation velocity. The conditions for the formation of a stabilized oblique detonation wave, initiated by the high-speed projectile both in free space and in the presence of a wedge surface placed at a certain distance along the projectile trajectory, are determined.

This paper presents a comparative study of the efficacy of fibrous and particulate reinforcement in titanium-matrix composites under high-speed mechanical loading. The structural and phase composition of the synthesized materials is investigated using synchrotron radiation. It is found that, during laser processing, fibrous reinforcing elements dissolve in the titanium matrix to a lesser extent than particulate powder particles. This causes a reduced volume fraction of the resulting secondary phases, such as TiC and Ti₅Si₃C_x when using SiC fibers, as well as TiB and TiB₂ when using boron fibers. It is demonstrated that the use of fibers in the formation of titanium-matrix composite coatings enhances the impact strength of the resulting materials.

This paper considers the laser additive manufacturing process using the heat conduction equation with an instantaneous point heat source. It is shown that, under certain limitations, the depth of the substrate melt pool is accurately described by a self-similar solution. Two-parameter correlations for the melt pool depth and width with the Peclet number (the ratio of the scanning speed to the thermal diffusivity) and the dimensionless enthalpy (the ratio of the specific energy absorbed by the material to the energy required for melting) are derived. Criteria for the occurrence of two melting modes - keyhole and conduction - are established. It is demonstrated that the derived analytical correlations are in good agreement with experimental data.

This paper describes the CCDS2000 detonation coating system and demonstrates its capability for depositing electrically insulating and wear-resistant aluminum oxide coatings. The dielectric strength of the coatings exceeds 25 kV/mm within a thickness range of 50-300 μm. The coatings exhibit an electrical resistivity ρ_e > 2.67 × 10¹³ Ω·cm at 20°C and a relative humidity of up to 59%. A further increase in humidity caused a sharp decrease in ρ_e by 2-3 orders of magnitude. The coatings exhibit adhesion to a steel substrate of 60-70 MPa, a microhardness value HV0.1 = 1522-1655, and a porosity of 0.35-1.00%. Evidently, the C₂H₂ + 2O₂ detonation mixture is optimal for obtaining electrically insulating coatings, whereas the 0.69C₂H₂ + 0.53C₃H₆ + 2.51O₂ mixture yields the best wear resistance. The use of the dual-fuel mixture results in a fourfold increase in abrasive wear resistance and a 34% improvement in erosive wear resistance.

This study investigates a friction stir welding process for joining high-strength aluminum alloys. By implementing an active liquid cooling system and a post-weld aging treatment, a weld strength equivalent to the base material is achieved. The effect of cooling intensity on the microstructure and mechanical properties of the welds is examined. Optimal welding parameters for producing equal-strength joints are identified.

This study investigates the contact interaction between a thin composite strip and the rolls during rolling, focusing on conditions that ensure a horizontally straight exit end. The values of friction coefficients required to maintain a straight exit end during asymmetric rolling of a multilayer metallic material are determined. A finite element modeling of asymmetric rolling of a five-layer composite is performed with varying friction coefficients on rolls. The tool-workpiece interaction is modeled using the Amontons-Coulomb friction law, with the friction coefficient ranging from 0.1 to 0.4. The results show that a friction coefficient of 0.2 on both rolls minimizes the curvature of the exit end, resulting in an almost perfectly straight strip. For this optimal case, the stress-strain state is analyzed and the linear velocity distribution across the strip in the rolling direction is investigated. The analysis suggests that, upon passing across the deformation region, all material points move at a uniform velocity, which is significantly lower than the peripheral velocity of the lower roll, indicating persistent slip of the strip at the lower surface of the roll.

This paper addresses key challenges in the numerical simulation of gas-particle flows relevant to aerodynamics. Results are presented on the flow structure of the dispersed phase and the associated energy flux to a body surface. Particular emphasis is placed on simulating stochastic phenomena, including inter-particle collisions, the scattering of non-spherical particles upon wall rebound, and particle polydispersity, which are characteristic of real flows, but neglected in classical gas-particle flow theory. The collisional gas of particles within the carrier gas is simulated using a kinetic approach coupled with the direct simulation Monte Carlo (DSMC) method. A three-dimensional model for non-spherical particle-wall collision is implemented, and the particle size distribution in the free stream is described by a log-normal law. Using this approach, the dispersed phase flow structure was investigated for high-speed gas-particle flow over a blunt body (specifically, transverse flow around a cylinder). Energy loss distributions upon impact with the surface are calculated for particles of different shapes. The influence of the shielding effect during particle collisions on the energy loss is also examined.

This paper presents a method for predicting the movement of the laminar-turbulent transition front on the side surfaces of spherically blunted circular cones with account for surface roughness effects. The study demonstrates that mass ablation of the composite thermal protection systems on re-entry vehicles induces surface roughness along the flight trajectory. This roughness arises from differential ablation rates between the constituents of the material, such as fillers and binders, reinforcing frame elements, and the carbon matrix.

Non-equilibrium molecular dynamics (NEMD) simulations are performed to investigate the viscosity and rheology of benzene and nanofluids containing carbon nanotubes of two diameters and varying lengths. The results demonstrate that these fluids exhibit pseudoplastic (shear-thinning) behavior with increasing shear rate. Correlations are established for the critical shear rates as a function of nanotube concentration and length. At high shear rates, the viscosity differences between the nanofluids and the base fluid decrease monotonically, irrespective of nanotube length. This is attributed to shear-induced changes in the momentum dissipation mechanisms within the system.

This paper presents combined experimental and numerical results on the interaction of shock waves with highly porous, permeable barriers featuring both homogeneous and inhomogeneous spatial structures. The experiments are conducted in a shock tube for shock Mach numbers ranging within M = 1.2÷1.8. The experimental barriers comprise stacked wire meshes with triangular cells and layers of cellular nickel foam. The numerical simulations are based on the Reynolds-averaged Navier-Stokes (RANS) equations, utilizing a toroidal skeletal model for the porous media. The results demonstrate that minimal shock wave reflection is achieved using graded barriers, which consist of a sequence of mesh layers with progressively decreasing cell size, capped by a layer of fine-pore nickel foam.

This paper presents numerical simulation results for supersonic turbulent airflow in a planar channel with a backward-facing step, incorporating a volumetric heat source that simulates the heat release from chemical reactions. The simulations account for conjugate heat transfer between the flow and copper plates mounted into the channel walls, which act as heat flux sensor elements. The results show that the heat source reduces the flow velocity and causes an upstream shift of the supersonic wave structure. Increasing the source power enlarges the subsonic zone transversely, induced by flow separation at the shock impingement location. A localized subsonic region forms in the flow core, isolated from the near-wall subsonic zone by a narrow supersonic jet, confining the thermal plume to the core flow. A sharp flow restructuring is triggered when the local separation zone merges with the recirculation zone downstream of the backward-facing step, allowing for the gas (warmed up by the heat source) to penetrate the enlarged separation bubble. This narrows the effective flow region, causing a compression wave, rather than an expansion wave, to form at the step edge. Consequently, the core flow temperature decreases while wall heat fluxes increase substantially.

The gas separation process via a membrane-sorption method шs investigated using a hydrogen-helium mixture and silica microspheres. Experimental and numerical modeling of a two-stage membrane-sorption process for hydrogen-helium mixture separation is carried out. The experimental two-stage separation at 22°C demonstrates an increase in the helium volume fraction from 10.5% in the feed to 57.8% after the first stage and 93.3% after the second stage. Evidently, the final helium volume fraction in the enriched stream is primarily influenced by the amount of depleted mixture remaining in the adsorber prior to the desorption cycle.

Quantitative thermography is used to study the effect of streamwise-orientated, quasi-two-dimensional roughness elements (strips) on the laminar-turbulent transition location on a 45° swept wing model under various test conditions. The efficacy of these sliding roughness elements for flow laminarization is investigated under elevated freestream turbulence levels and increased surface roughness. The results demonstrate that this laminarization method is also robust to moderate variations in the freestream velocity.

This paper presents an experimental investigation of how heat release from homogeneous condensation in a supersonic expanding flow affects the density distribution and shock structure of underexpanded rarefied-gas jets. The results demonstrate that this effect is significant for modeling the force and thermal loads imposed by attitude and control thrusters on adjacent spacecraft components.

We present the SUNSHYNE software package, designed for numerical simulation of compressible gas flows on modern high-performance computing systems, including those accelerated by high-performance graphics processing units (GPUs). The package features a graphical user interface and enables simulations in complex geometries for industrial applications. This is facilitated by versatile boundary condition specification, support for unstructured and block-structured grids, and integration with computer-aided design systems. The paper touches upon the implemented physical models, numerical methods, and functional capabilities of the package. Example simulations are provided, including non-equilibrium flows, direct numerical simulation of transition to turbulence, and heterogeneous detonation.

We develop and implement a numerical model for the dynamic fracture of a functionally graded material (FGM) plate based on St.3 steel and VT8 titanium alloy under shock-wave loading. The simulations employ a three-dimensional finite element formulation within the EFES software package. A mixing parameter is introduced to model the smooth transition in material properties across the plate thickness. A Taylor-type numerical test and a simulation of aluminum projectile impact on a graded barrier are conducted to assess residual deformation, pressure profiles, and spall formation conditions. The St.3 → VT8 gradient direction effectively dissipates the shock wave and suppresses spallation, whereas the reverse gradient causes tensile stress localization and spall fragment formation. The numerical spall thickness values show good agreement with experimental data, confirming the model's adequacy for predicting the dynamic strength of functionally graded structures under high-rate loading.

This paper proposes a mathematical model within the class of generalized continua that account for an internal microstructure. The model considers the inhomogeneous deformation of an infinitesimal volume element. It incorporates plastic slips at the interfaces between these volume elements. Unlike classical continuum mechanics, the formulation introduces additional kinematic degrees of freedom. In the planar case, these are represented by two independent smooth displacement fields, which introduce a length-scale parameter into the constitutive equations, characterizing the internal structure of the medium. The model is applied to numerically solve the problem of stress redistribution in the near-field zone of a system of mine excavations in a rock mass, induced by a specific mineral extraction technology. The results demonstrate that accounting for the material microstructure, which is a feature absent in classical elastoplastic models, shifts a significant portion of the load from the excavation boundaries deeper into the rock mass.

This study determines the mechanical parameters of ABS plastic (acrylonitrile butadiene styrene) by subjecting plates of finite thickness (1-5 mm) to impact loading. A spherical lead particle with a mass of 0.45 g serves as the projectile. A series of experiments provides the basis for mathematical modeling performed with the Reactor3D software package. The results show that the 0.45 g spherical projectile perforates a 3.5-mm-thick ABS plastic plate at an impact velocity of at least 230 m/s. The required impact velocity for perforation ranges from 140 to 300 m/s for ABS plates with thicknesses of 1 to 5 mm. The parameters obtained in this study describe the behavior of finite-thickness plates under impact with an error of less than 5%.

This study assesses the potential for replacing expensive alloys with novel metal-matrix composites comprising more accessible materials. It compares the dynamic response of the widely used VT20 aviation titanium alloy with that of a 316L steel - A356 aluminum metal-matrix composite under impact loading.

This study investigates the mechanoluminescent properties of epoxy resin composites filled with SrAl₂O₄:Eu,Dy (SAOED) phosphor. The elastic modulus of this phosphor is measured. The relationships between the mechanoluminescent intensity and mechanical loading parameters are characterized. The composites exhibit repeatable mechanoluminescence under cyclic mechanical stimulation.

This review surveys the development of hydrophobic and anti-icing coatings fabricated by cold gas dynamic spraying. It discusses fabrication strategies for achieving high hydrophobicity and icephobicity with cold gas dynamic spraying, covering coatings based on polymeric, metallic, and ceramic materials. A key advantage of cold gas dynamic spraying is its ability to create coatings with complex microstructures that confer high hydrophobicity and icephobicity without the need for post-processing. The review also covers the fundamental theoretical models of wetting and the key factors governing surface icephobicity.