THERMODIFFUSION SATURATION OF THE SURFACE LAYERS OF α-TITANIUM BY OXYGEN, NITROGEN, CARBON

The purpose of the study is to analytically assess the depth of the gas-saturated zone in the case of a single-component diffusion saturation of alpha-titanium with nitrogen, oxygen and carbon from a rarefied controlled gas environment. Results. Based on the analysis of the literature data, the work schematically shows the interaction of alpha titanium with the elements of implementation and presents the processes with the corresponding parameters that characterize. It is shown that the surface impurity concentration is equal to the equilibrium concentration and is established instantly and does not depend on time. Consequently, with the proposed generalized nonstationary boundary condition in the absence of diffusion of impurities into the volume of the metal, the time dependence of its surface concentration is given, determined by the intensity of surface processes. The dependence of the relative change in the microhardness in the diffusion zone of titanium due to dissolved nitrogen (without taking into account the contribution of nitride inclusions) is presented. Analytically calculated concentration profiles of nitrogen generally correlate well with the distribution of the corresponding relative changes in microhardness in the surface layer. Analytical calculations of the concentration profiles of oxygen, nitrogen and carbon in titanium at a saturation temperature of 700 °C are presented. Practical value. The results obtained will make it possible to preliminarily estimate the size of the fortified near-surface layer depending on the parameters of chemical-thermal treatment and select the optimal parameters of thermal diffusion treatment to ensure the formation of reinforced layers on products made of alpha-titanium based on elements of interstitial in order to increase the functional properties.

Piecewise linear approximation of boundary conditions and solutions in problems of 1d nonstationary dynamics of heteromodular elastic media

Рассматривается динамика одномерных деформаций разномодульной упругой среды под действием нестационарной граничной нагрузки в режиме «растяжение - сжатие». Исследуются особенности построения кусочно-линейной функции, аппроксимирующей нелинейное краевое условие. Указан критерий выбора узловых точек разбиения аппроксимирующей функции, позволяющий управлять режимами взаимодействия волновых фронтов всех типов в решении краевой задачи. Получена итерационная формула изменения скорости ударной волны в результате ее попутного столкновения с медленными фронтами предварительного растяжения, а также итерационные соотношения для построения поля перемещений на всех стадиях деформирования. The one-dimensional deformation dynamics in an elastic heteromodular medium under nonstationary boundary loading in the <tension and compression> mode is considered. The features of constructing a piecewise linear approximation of a nonlinear boundary condition are investigated. A selection criterion for the nodal partition points of the approximating function is indicated; it allows us to control the modes of collision between wave fronts of all types when the boundary value problem is solved. An iterative formula for the change in the shock wave velocity as a result of its collision with slow fronts of preliminary tension is obtained; the iterative relations for constructing the displacement field at all stages of deformation are written.

Application of Immersed-Boundary Method to Complex Geometry Flows With Heat Transfer

In the present study, an immersed-boundary method is adopted to simulate natural and forced convection within a domain with complex geometry. The method is based on the direct momentum and energy forcing on a Cartesian grid and issues involving implementation of both the thermal (Dirichlet and Neumann) and dynamic (stationary and nonstationary) boundary conditions are addressed. The second order accuracy of the present method was validated based on natural convection in an annulus between horizontal concentric cylinders. Simulations of flow over a stationary cylinder with heat convection were further conducted to validate the capability of present technique for both temperature boundary conditions. Finally, the influence of the lock-on phenomenon in heat transfer is investigated for flow over a transversely oscillating cylinder. All computed results are in generally good agreement with previous experimental measurements and numerical simulations.