Journal of Applied Mechanics and Technical Physics最新文献

A passive method for reducing the drag of a cylinder by placing a flat plate behind it at a Reynolds number Re=10⁵ has been studied. The paper presents the results of an ANSYS Fluent simulation of the flow around a cylinder–plate system, including the velocity and pressure fields, streamlines, and the dependences of the drag coefficient and the position of the separation point on the surface of the cylinder on the relative length of the plate. It has been found that the drag coefficient of the cylinder–plate system can be reduced by approximately 40% compared to the case of an isolated cylinder.

The formation of a mixed-type (fracture modes I and II) internal crack in a pipe wall that is made of an ideal elastoplastic material under the action of combined tensile (compression) and bending loads is described. The fracture of such materials is illustrated using a modified Leonov–Panasyuk–Dugdale model, which additionally uses the parameter of fracture process zone diameter. Another case under consideration is complex loading during which the crack path becomes curved, so its bend angle is determined using a force integral criterion based on the stress field asymptotics in the vicinity of the crack tip. Critical fracture parameters are obtained using a two-parameter (dual) strength criterion in the case of a complex stress state. The parameters included in the resulting analytical model are analyzed. The dimensionless geometric parameters of the structure are obtained numerically using the finite element method. Quasibrittle fracture diagrams are constructed.

A linear theory of static cylindrical bending of a thin plate is constructed without using the Kirchhoff hypotheses. Transverse shear, thickness compression, and the resulting longitudinal force are taken into account. In view of changes in the areas of both surfaces during bending, the transverse distributed force is determined. It is assumed that the average pressure on the plate is several orders of magnitude greater than the pressure difference. Bending is considered under the conditions of a plane strain state and a stress state.

This paper describes a numerical simulation within the framework of a two-dimensional shallow water model of interaction of a solitary wave with a steady rectangular semi-submerged structure. The results of this study are compared with the results of calculations based on a model of irrotational three-dimensional flows, and it is shown that the simulation accuracy at small incident wave amplitudes is satisfactory. It is also revealed that, the solitary wave diffraction on the cylinder surface is neglected when using a one-dimensional shallow water model, then the maximum values of wave runup on the edge of the cylinder and the force loads on it become overestimated.

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.