Journal of Applied Mechanics and Technical Physics最新文献

Streamwise structures generated by external vortical and thermal waves in subsonic and supersonic boundary layers have been studied. Particular attention is paid to the formulation of the boundary conditions at the outer edge of the boundary layer. It has been found that the disturbances of the boundary-layer streamwise velocities can be several times larger than the amplitude of the external vortical wave. The generation efficiency decreases with increasing Mach number. It has been shown that the influence of thermal external waves on the boundary-layer flow structure is much weaker than the influence of the vortex structure of the flow.

This paper describes a study of deformation of an ideal elastoplastic adhesive layer of a sample in the form of an elastic double-cantilever beam. The (J) integral values are determined for a number of adhesives with account for all diagonal stress tensor components in the layer. It is shown that the (J) integral value is significantly affected by the plane problem type in the case where an elastic-plastic model of layer deformation is applied. As demonstrated in the study, compressive stresses may be present during normal fracture in the irreversible deformation region of the adhesive in a plane stressed state.

This paper is devoted to the influence of substrate preheating on the structure of cermet coatings made of TI–6AL–4V alloy reinforced with B₄C particles using direct metal deposition. Coatings with a 15% mass fraction of B₄C were obtained for the first time. It is shown that substrate preheating makes it possible to produce cermet coatings without cracks. In tribological tests, the wear scar volume of the cermet coating decreased by a factor of eight compared to the coating with a 10% mass fraction of B₄C.

The physical processes of crystallization of melt drops in water were studied using the drop granulation and melt centrifugation methods. A mathematical model was developed to determine the cooling and crystallization rates and structural dendritic parameter for aluminum alloy granules based on the initial data of the process, the diameter of melt drops, and cooling conditions. Predicting the dendritic parameter of the microstructure of granules makes it possible to predict the level of microstructure dispersion and hence the strength properties of the granulate material. The model parameters take into account the drop speed, features of heat removal processes, and the temperature dependence of the thermophysical parameters of the media. An application program implementing the developed mathematical model was developed. The developed mathematical model was implemented using the Microsoft Visual C++ programming language. The mathematical model was tested for the granulation of high-alloyed aluminum alloys (D1 and D16 alloys of the Al–Cu–Mg system, and B95 and B96Ts alloys of the Al–Zn–Mg–Cu system) obtained by centrifugal melt spraying and the drop method with cooling in water. Crystallization rate in full-scale samples was measured based on an analysis of the structural dendritic parameter of the material. Analysis of the calculated values of the dendritic parameter and its measurements for real granule samples shows good convergence of the simulation and measurement results.

A description of a small icing wind tunnel designed for studying the icing processes at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences is presented. The use of such a wind tunnel offers a possibility not only of studying the physical features of the icing process, but also of testing methods of anti-icing control, validating numerical methods used for calculating the icing processes, etc.

The deposition process of a nickel-based cermet coating with a high (60 wt.%) mass content of tungsten carbide was investigated. The results showed preheating the substrate to 500°C prevented the formation of cracks and pores in the coating. This is because preheating reduces the thermal shock between the substrate and the coating, leading to better adhesion and fewer defects. Additionally, synchrotron radiation was used to analyze the phase composition of the resulting composite. It was found that additional heating of the sample to 500°C during surfacing did not cause significant changes in the phase composition of the composite.

This paper presents a solution to the Gadolin problem of the evolution of stressed states in the shrink-fit assembly of two cylindrical pipes. The materials of the assembly parts are described using the mathematical model of an ideal elastic-viscoplastic material. The friction law is specified on the contact surface of the materials of the assembly. The yield criterion is taken to be the maximum octahedral stress criterion (von Mises criterion) in which the yield stress depends significantly on the local temperature. Time-varying thermal stresses are calculated in successive time steps, depending on the temperature distribution reached by that time. The calculated residual stress and fit interference in the assembly are compared with the values obtained from a numerical-analytical solution of the one-dimensional problem. Differences in the behavior of the fit interference in the near-end region of the structure due to the neglect of the singularity in the boundary conditions are noted.

This paper describes a numerical study of the equilibrium parameters of a one-dimensional chain consisting of three dust particles levitating in the electric fields of a gas-discharge plasma. A numerical model is considered in which the movement of dust particles is simulated with account for the action of the Coulomb repulsion force, external electric field, gravity, electrostatic force induced by a plasma space charge, and ion drag described analytically. The spatial distributions of the plasma space charge are compared with a potential around dust particles and the equilibrium structural parameters of a dust chain, depending on the fact whether the ion drag is taken into account analytically or not. It is shown that, when the ion drag is taken into account analytically, the dust chain as a whole is displaced in the direction of the ion flow. In this case, the distances between the dust particles turn out to be smaller than in the case where the ion drag is neglected.

Dimensionless parameters and scaling laws that describe the geometric dimensions of a cermet weld bead formed during direct metal deposition are determined. A Ti64 titanium alloy and ceramics (silicon carbide, SiC) with different volume fractions are used as a powder mixture. A model for estimating the thermophysical parameters of a heterogeneous material is proposed. It is shown that, regardless of the volume fraction of ceramics, the dimensionless geometric parameters of a single track (depth, width, and height) depend on two dimensionless parameters: normalized enthalpy and the Peclet number. Also, these dependences can be approximated by algebraic expressions.

The problem of instantaneous injection or withdrawal of Newtonian fluid through an injection or production well into an infinite reservoir with a vertical main fracture of constant width at a given constant bottomhole pressure and constant reservoir pressure is considered. Analytical solutions are obtained for the pressure fields in the fracture and the reservoir during injection or withdrawal of fluid, as well as for the flow velocity in the fracture. An explicit expression for the leak-off (leak-in) of fluid from the fracture into the reservoir (from the reservoir into the fracture) and equations of particle trajectories in the fracture and reservoir are obtained. For the solutions obtained, graphs are plotted for the pressure fields, fluid velocity distributions in the fracture, and fluid leak-off from a finite fracture into a finite reservoir for different reservoir permeabilities.