Journal of Applied Mechanics and Technical Physics最新文献

We report an experimental study of the wear and fracture of ZrN-coated VT6 alloy in its coarse-grained (as-prepared) and ultrafine-grained states during high-rate dynamic erosion by solid corundum particles with an average size of 109, 58, and 23 μm in an air flow at velocities in the range 50–250 m/s and exposure times of 30, 60, and 300 s. The experimental data were used to determine the fraction of viscous fracture, the erosion damage depth, the change in the microstructure of the coated and uncoated alloy near the erosion surface, and also the weight wear and surface roughness. The results demonstrate that, in the case of high-rate erosion, the alloy wear and damage processes depend significantly on the exposure time, erosion rate (velocity of abrasive particles), powder particle size, and substrate structure.

The cavitation process in a pulsed focused ultrasound field is studied. An abnormally long (up to several minutes) delay in the onset of inertial cavitation relative to the moment of ultrasound activation is recorded for the first time. A method for selecting field parameters that enable control over the cavitation region dynamics is proposed.

Adiabatic and isothermal wall boundary conditions with slip and temperature jump are implemented and applied using the HyCFS-R code for simulating near-continuum flows. Validation is performed on external and internal flow problems. The flow around a T2-97 hollow cylinder flare is chosen as the external flow, and shock wave propagation in a long tube and low Reynolds number nozzle flow as the internal flow. It is found that for flow around a hollow cylinder flare, the implementation of slip boundary conditions leads to better agreement with experimental data on the positions of the flow separation and reattachment points than no-slip conditions. In the calculation using slip boundary conditions, the shock wave is found to propagate along the long tube faster than in the calculation using no-slip boundary conditions. The calculated shock wave propagation velocities are in satisfactory agreement with the experimental data. In the case of nozzle gas flow, the use of slip boundary conditions leads to better agreement between the calculated and experimental surface temperature distributions.

Filtration equations are used to address the problem of CO₂ injection into a viscoelastic porous medium. We examine a two-dimensional problem of deformation of a porous skeleton, taking into account porosity changes. An exact solution to an initial boundary value problem in a thin layer is found for a model system of equations.

Abstract—Mathematical models of long-wave approximation for a three-layer fluid are considered taking into account mixing and entrainment at the interfaces of the layers. These nonlinear models are used to describe changes in the nature of non-uniform flows when passing over localized elevations of the bottom. Comparison of the results of numerical calculations with the data of field measurements shows that the models adequately reproduce the structure of shelf and deep-water currents, in which the flow splits with subsequent thickening of the passive intermediate layer and formation of an intense inclined jet behind an obstacle.

We report physical modeling of the forming process for a panel from AK4-1 (Al–Cu–Mg) alloy under creep conditions at an annealing temperature of 420°C. The forming process was imitated by creep tension of circular cylindrical specimens to various strain levels no higher than 6%. Creep test results were used to determine parameters of the Boyle–Norton classic model for steady-state creep. In accordance with the forming process under creep conditions, the specimens were heat-treated (quenching and aging) in order to restore the strength properties of the panel. The stress for fatigue tests was determined using stepwise cyclic loading with increasing stress amplitude. The tests were stopped when plastic deformation was observed. We compared fatigue failure resistance characteristics of as-received specimens, specimens stretched upon creep and after heat treatment, and specimens with zero creep strain after heat treatment. Our results demonstrate that accumulated creep strain above 2% can lead to a decrease in the fatigue characteristics of the specimens in comparison with those of the as-received specimens.

Results of a study on the accuracy of mathematical modeling of plastic metal flow using the finite element method implemented in various software products are reported. The shortcomings of the finite element method and their impact on the description of deformation processes occurring during intensive shape change of workpieces are studied. Particular attention is paid to the study of regions with complex metal flow. The parameters of real products are compared with the results of mathematical modeling obtained using MSC Simufact.Forming, Transvalor Forge, SFTC DeForm, and QForm. Evidently, the results of mathematical modeling obtained using these software products in the study of complex metal flow are sufficiently accurate.

We have investigated the mechanism responsible for aluminum (Al) coating growth on a titanium (Ti) substrate during cold gas spraying. Examination of the structure of coatings produced by the cold gas spraying method has shown that they contain a rough transition layer in which the Al and Ti atoms are intermixed. We assume that the formation of the transition layer is the result of collisions of microparticles with the rough substrate surface and is due to a convective mechanism. In simulating the intermixing process by the smoothed particle hydrodynamics method, we have numerically solved the problem of collision of an Al microparticle with a Ti substrate having a conical pit. The results point to the formation of a cumulative Al jet, which penetrates the Ti substrate, cools, solidifies, and stays in it in the form of an aluminum inclusion. Collisions of a large number of microparticles with the substrate lead to the formation of a transition layer with a reduced activation energy for the formation of bonds between atoms of the Al microparticles and Ti substrate. Colliding with the transition layer, Al microparticles can attach to its surface to form aluminum coating.

A fiber laser and post heat treatment have been used to produce high-strength laser welded joints of Al–Cu–Li alloy. The structure–phase state of the weld seams has been studied by synchrotron X-ray diffraction in transmission geometry, and data have been obtained on the structural and phase compositions of the weld seams as three-dimensional objects. We have studied the effect of heat treatment on the fatigue resistance of laser welded joints of aluminum–lithium alloy of the Al–Cu–Li system and performed static mechanical tests of the laser welded joints at a normal, an elevated, and a reduced temperature in order to assess the strength and deformation properties of the Al–Cu–Li system. Welded joints of the Al–Cu–Li system have been dynamically tested in impact toughness by the Charpy method.

We solve a problem of forced flexural vibrations of a strip-like rod with two cantilevers and a finite-length bonded region on one of the outer surfaces. The classical Kirchhoff–Love model is used to describe the cantilever deformation processes, while the deformation of the bonded region is investigated using a refined Timoshenko shear model with account for transverse normal strain, modified by allowing for prescribed motions of the supporting element. We formulate kinematic conditions for coupling the bonded region with the cantilevers. These conditions are applied to derive equations of motion and boundary conditions, as well as force continuity conditions at the junctions of the rod regions, on the basis of the Hamilton–Ostrogradsky principle. An exact analytical solution is constructed for the problem of harmonic forced vibrations under the action of a harmonic transverse force at the end of one of the rod cantilevers. Numerical experiments are performed to study the forced flexural vibrations of a D16AT duralumin rod. Evidently, the vibrations of the unloaded rod cantilever are mainly caused by the prescribed motions of the supporting element.