Journal of Applied Mechanics and Technical Physics最新文献

The contact interaction between a thin composite strip and rolls during rolling is studied in the case where the exit end is maintained in a horizontal position. The friction coefficient values required for a straight exit end in asymmetric rolling of a multilayer metallic material are determined. Asymmetric rolling of a five-layer composite is simulated for different friction coefficients on the rolls. The tool–workpiece interaction is described by the Amontons–Coulomb friction law, with the friction coefficient varying from 0.1 to 0.4. The results show that for a friction coefficient of 0.2 on both rolls, the exit end of the strip has minimum curvature, remaining almost straight. For this case, a stress-strain analysis is performed and the linear-velocity distribution across the strip in the rolling direction is investigated. It is shown that after passing through the deformation zone, all material points move with the same velocity far below the linear velocity of the lower roll, indicating a continuous slippage of the strip on the bottom surface of the roll.

This paper presents a method for calculating the movement of the laminar–turbulent transition front along the sidewalls of flight vehicles with the shape of spherically blunted circular cones taking into account the influence of roughness. It is shown that the ablation of composites used in thermal protection systems of reentry vehicles moving along a trajectory leads to the occurrence of surface roughness due to the different ablation rates of fillers, binders, reinforcing elements, and carbon matrix of the composites.

We have studied mechanoluminescent materials based on epoxy resin loaded with SrAl₂O₄:Eu,Dy (SAOED) phosphor. Elastic characteristics of the phosphor have been determined experimentally, and the mechanoluminescence intensity has been measured as a function of loading parameters. Experimental evidence is presented for sequential photoluminescence decay in the materials during cyclic loading.

We have studied gas separation by the membrane sorption method, exemplified by hydrogen–helium mixtures, with the use of silica microspheres. A two-stage process for membrane sorption separation of hydrogen–helium mixtures has been modeled experimentally and numerically. Experimental modeling of the two-stage process for hydrogen–helium mixture separation at a temperature of 22°C has shown an increase in the volume fraction of helium from 10.5% in the starting mixture to 57.8 and 93.3% in the enriched mixture after the first and second stages of the gas separation process. The amount of the lean mixture in the adsorber before the beginning of the desorption process has been shown to have the main effect on the final volume fraction of helium in the enriched mixture.

In this paper, we present results of a comparative study of the efficiency of fiber and particle reinforcement in titanium-matrix composites subjected to high-speed mechanical loading. The structure–phase composition of the synthesized materials has been studied using synchrotron radiation. The results demonstrate that, in the case of laser processing, the degree of dissolution of reinforcing fiber is lower than that of fine powder particles. This leads to a decrease in the volume fraction of the forming secondary phases, such as TiC and Ti₅Si₃C_x, in the case of SiC fiber, and such as TiB₂ and TiB in the case of boron fiber. The use of fiber in producing titanium-matrix composite coatings has been shown to ensure an increase in the impact resistance of the coating material.

A mathematical model from the class of generalized media possessing an internal microstructure is proposed. The model considers the nonuniform deformation of an infinitesimal elementary volume, where plastic shears at the volume boundaries are taken into account. Unlike the classical description of a continuum, additional kinematic degrees of freedom are introduced; in the planar case, these are described by two independent smooth displacement fields. This leads to the fact that a length-dimensional parameter that characterizes the structure of the medium is introduced into the constitutive equations. This model is applied to numerically solve the problem of stress redistribution in the near-boundary region of a system of mine workings within a rock mass, arising from the application of a specific mining technology. It is revealed that accounting for the microstructure of the medium—a feature absent in classical elastoplastic models—results in a significant transfer of the load from the working boundaries deeper into the deformed medium.

A numerical model was developed and implemented to describe the dynamic fracture of a plate made of a functionally graded material based on St.3 steel and VT8 titanium alloy under shock-wave loading. Numerical simulation was performed by a three-dimensional finite element using the EFES software. To describe the properties of the functionally graded material, a mixing parameter is introduced that ensures a smooth transition between the materials across the plate thickness. A numerical test similar to the Taylor test and a simulation of the impact of an aluminum projectile on a continuously functionally graded target were performed to evaluate residual strains, pressure profiles, and the conditions for the onset of spall fracture. It is found that the St.3 ( to ) VT8 gradient provides effective shock-wave dissipation and suppression of spall fracture and the opposite gradient leads to the localization of tensile stresses and the formation of a spall fragment. The numerically obtained values of the spall thickness are in good agreement with the experimental data, which confirms that the proposed model adequately predicts the dynamic strength of functionally graded structures under high-velocity loads.

This paper addresses several problems in the numerical simulation of dusty gas flows pertaining to aerodynamics. We present results of an investigation of the flow structure of the dispersed phase and the energy flux toward the surface of a body. Primary attention is given to simulating random phenomena—particle collisions, scattering of nonspherical particles upon rebound from the surface, and particle polydispersity—which are characteristic of real flows but are not accounted for in the classical dusty gas flow theory. A kinetic model and the direct simulation Monte Carlo method are used to calculate the so-called “collisional gas” of particles within the carrier gas flow. A three‑dimensional model of nonspherical particle–wall collision is employed. The particle size distribution in the unperturbed flow is described by a log–normal law. Within the framework developed, the flow structure of the dispersed phase is investigated for a high‑speed dusty gas flow over a blunt body; i.e., a transverse flow around a cylinder is considered. The energy–loss distribution during collisions with the surface is calculated for particles of various shapes. The influence of the schielding effect during particle collisions on energy loss is examined.

Additive laser deposition technology is analyzed using the heat equation for a system containing an instantaneous concentrated heat source. The results demonstrate that, with some limitations, the fusion penetration depth in the substrate is described by a self-similar solution with sufficient accuracy. We have obtained two-parameter dependences of the fusion penetration depth and width on the Peclet number (ratio of the scanning speed to the rate of change in the temperature of the material) and dimensionless enthalpy (ratio of the specific energy absorbed by the material to the energy needed for melting) and found criteria for whether the knife fusion penetration or heat conduction regime will take place. The analytical relations we obtained have been shown to describe experimental data with sufficient accuracy.

This paper presents the results of numerical simulation of supersonic turbulent air flow in a planar channel with a backward-facing step in the presence of a volumetric heat source of specified power, which models heat release from chemical reactions. The calculations account for conjugate heat transfer between the high-velocity flow and copper plates (sensing elements of heat flux sensors) embedded into the channel walls. It is shown that the presence of the heat source leads to a decrease in the flow velocity within the channel and an upstream shift of the wave structure of the supersonic flow. Amplifying the source power increases the transverse size of the subsonic zone due to flow separation in the region where the shock wave impinges. A localized subsonic zone forms in the flow core, separated by a narrow supersonic jet from the near-wall subsonic zone. In this regime, the thermal wake of the source is located within the flow core. It is revealed that an abrupt change in the flow structure occurs when the local separation zone merges with the recirculation zone behind the step, causing gas heated by the source to enter the extensive separated region. This results in a narrowing of the effective cross-sectional area, leading to the formation of a compression wave at the step corner instead of a rarefaction wave. Consequently, the temperature in the flow core decreases, while the heat fluxes on the walls increase significantly.