Journal of Applied Mechanics and Technical Physics最新文献

The behavior of a material under laser surface treatment taking into account melting is described. A Maxwell model accounting for the changes in heat capacity and viscosity with changing temperature and material composition is presented. Based on this model, a model describing the change in the properties of a flat layer material subjected to a moving heat source is developed. An algorithm for the numerical solution of the formulated problem is presented. Examples are given showing the effect of heat loss, coupling, melting, chemical reactions, and their acceleration due to the stress work on the properties of the material.

A simplified numerical method for simulating projectile penetration into fabric targets is proposed which takes into account the weavearchitecture, inter-yarn friction, projectile–fabric friction, and the transverse dimensions of the fabric. The necessary design parameters were selected from a comparison of experimental and calculated data. The proposed method was used to estimate the ballistic resistance of a composite armor reducing the after-penetration effect. The influence of the projectile shape on the ballistic resistance of fabric armor was investigated.

A grid-characteristic numerical method based on tetrahedron grids is applied to simulate wave processes in a composite material under the action of a pulsed shock load. An approach is proposed to increase the approximation order of the method on an unstructured grid in the three-dimensional case. Computational results for load pulse propagation in a three-layer composite are presented.

Ceramic composites based on B₄C with a CrB₂ mole fraction of 0–30% were obtained by reactive hot pressing of a mixture of B₄C, Cr₂O₃, and nanofibrous carbon at a uniaxial pressure of 17.5 MPa and a temperature of 2000 °C for 10 min. The possibility of boron carbide reduction of metal oxide during hot pressing was studied. During the synthesis of CrB₂, the density of B₄C was found to increase due to the formation of the CrB₂–B₄C eutectic liquid phase. The relative density of all B₄C–CrB₂ composites obtained under these conditions exceeds 90%. Experimental dependences of the microhardness and elastic modulus of samples on the concentration of the CrB₂ plastic phase were obtained. The dependences of the elastic modulus of the heterogeneous material on the volume fraction of chromium diboride were determined taking into account porosity by sequentially using the Reuss and Voigt averaging schemes.

Crystal 85-5 epoxy resin modified with MHG-4E photoluminescent powder (average particle size 5–15 (mu)m) and FV-530D photoluminescent powders (average particle size 25 (mu)m) photoluminescent powders were studied by mechanical uniaxial tension and three-point bending tests. The dependence of the elastic modulus on filler concentration was obtained. The photoluminescent properties of the resulting composites were examined. The dependence of the afterglow intensity on filler content in the composite was determined.

Optimization of tangential jet blowing on the upper surface of a supercritical transonic airfoil under buffet conditions was carried out. Two-dimensional unsteady Reynolds-averaged Navier–Stokes equations were solved to simulate the flow past the airfoil. The Spalart–Allmaras turbulence model was used to close the equations. The location of the slot nozzle and the intensity of the jet blowing from it were varied. The optimal location for blowing with minimum jet intensity to suppress buffet was determined.

A problem of mathematical simulation of a fuel element region, including many fuel pellets and a cladding fragment, is considered in an axisymmetric formulation. It is assumed that the cladding is a thermoelastic-plastic body and that the pellet is a thermoelastic body with account for cracking of the material. Different variants of the domain decomposition method are used to numerically simulate the thermal and mechanical contact of pellets with each other and with the cladding. Calculation results are presented, in which the region containing ten pellets reaches a nominal power and the effect of pellet cracking on the thermomechanical state of the fuel element is estimated.

Investigations (mainly those performed by the authors) of air blowing through a perforated section on a body of revolution with a large aspect ratio in an axisymmetric incompressible flow are summarized. Result of numerical and experimental studies of the flow properties, efficiency of the turbulent boundary layer control and prospects of using it for a body of revolution at low subsonic velocities equivalent to the take-off and landing regimes for a modern subsonic cargo aircraft are analyzed.

This paper describes a new method for performing the time-frequency analysis of particle image velocimetry data with account for surface constant-temperature anemometer sensor readings. This method is based on calculating correlation coefficients between particle image velocimetry data and constant-temperature anemometer data, previously filtered in a given frequency range. This approach makes it possible to obtain data on the unsteady characteristics of flows throughout the entire measurement range in a frequency range whose boundaries extend beyond the boundaries of the particle image velocimetry frequency range. The proposed method is applied to study nonstationary processes in a region where a shock wave interacts with a boundary layer at a Mach number M = 1.43.

This paper presents the results of a study of the influence of various sources of magnetic field on the size of droplets formed in microfluidic flows. Direct and reverse emulsions in a microfluidic flow focusing were obtained using magnetic fluids based on oil and water which are a continuous phase. Non-magnetic inclusions of various volumes were formed depending on the selected parameters: continuous phase flow rate, magnetic field configuration, and the position of the magnet relative to the axis of the device.