Analysis of the stressed state of bodies with multilayer thin coatings

We develop a procedure for the analysis of the stress-strain state of structural elements with thin multilayer coatings based on the simulation of these coatings by shells with the corresponding geometric and mechanical characteristics. In this approach, the influence of coatings on the mechanical state of the entire body-coating system is described by special generalized boundary conditions. The efficiency of the proposed approach is demonstrated by comparing the results obtained by using the developed approximate procedure with the exact solution of a Lamé test problem of loading of a solid cylinder with n-layer coating. Pidstrygach Institute of Applied Problem in Mechanics and Mathematics, National Academy of Sciences of Ukraine, Lvov, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 136–150, January–February 2000.     

Conjucate heat transfer and thermostressed state of a plate with radiation and conduction heating

The problem of combined analysis of the parameters of conjugate heat transfer and thermostressed state of a plate with its radiation and conduction heating in an absorbing-medium layer is considered. The effect of the optical characteristics of the medium on the parameters of conjugate heat transfer and the distribution of thermal stresses in a plate is studied. Dnepropetrovsk State University, Dnepropetrovsk, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 1, pp. 79–84, January–February, 1996.     

Thermoelastic state of a thermosensitive hollow sphere under the conditions of convective-radiant heat exchange with the environment

The solution of the nonstationary problem of heat conduction is constructed for a thermosensitive hollow sphere in the process of convective-radiant heat exchange with media kept at constant temperatures. In this case, it is assumed that the heat-transfer and emissivity coefficients of the surfaces are functions of temperature. We study the influence of the thermal sensitivity of the material of the sphere on the intensity and character of distribution of temperature and the components of the stress-strain state. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 6, pp. 39–48, November–December, 2006.     

The effect of variable properties on the helical flow and heat transfer of power law fluids

Summary Laminar flow and forced convection heat transfer of the time independent non–Newtonian fluid obeying power law stress-strain relation have been investigated numerically in the annular space between two coaxial rotating cylinders. The problem is considered when the inner cylinder rotates about the common axis with constant angular velocity and the outer cylinder is at rest. The viscosity of the fluid and thermal conductivity are assumed to vary with the temperature. The outer surface of the annulus is considered to be adiabatic, while the inner surface has a uniform temperature. The tangential and axial momentum equations and energy equation have been solved iteratively by using a finite difference method. For the steady fully developed flow, the velocity distributions, temperature profiles, the volumetric flow rate, torque and the average Nusselt number have been obtained for different values of the radius ratio and model parameters.     

Unsteady frictional heating of projections of microirregularities of a sliding contact

A nonstationary mixed problem of heat conduction that models the process of frictional heating in sliding of rough surfaces is solved. I. Franko L'vov State University, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 5, pp. 768–772, September–October, 1996.     

Temperature displacements in naturally twisted turbine blades under conditions of nonuniform heating

We deduce and analyze design-basis formulas for the evaluation of the degrees of temperature torsion, temperature deflections in the planes of minimum and maximum stiffness, and temperature elongation of the pen of a naturally twisted turbine blade under the conditions of nonuniform heating. We present a practical example of the numerical calculations of temperature displacements in the peripheral section of the pen of a blade subjected to thermal cycling. In this case, the process of nonuniform heating of the naturally twisted blade is performed by a gas flow with cyclically varying temperature. To find the temperature fields in sections of the blade, we determine the local heat transfer coefficients along the perimeter of the profile separately for the periods of heating and cooling. Institute of Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 116–124, July–August, 1999.     

Dynamics of uniaxial tension of a viscoelastic strain-hardening body in a system with one degree of freedom. Part 1. Prescribed motion

The behavior of an open mechanical dissipative system formed by a viscoelastic hardening body and an elastic working element used for the energy transfer between the testing machine and the deformed body is described by a third-order dynamic differential equation with controlling parameters that depend on the reduced mass and stiffness of the system, its viscous resistance, the degree of strain hardening, the type of the stressed state of the body, and the dissipation of energy in a viscous ambient medium. We analyze the dynamics of uniaxial tension of the deformed body below and above its elasticity limit for the case where the forces induced in the process of motion are determined by the kinematics of the testing machine with prescribed motion. We establish the dynamic nature of the nonlinear section of the tensile stress-strain diagram beyond the elasticity limit of the viscoelastic body corresponding to the so-called “nonlinear elasticity”. It is shown that the appearance of this section is connected with a transient relaxation process. Upon the termination of this process, the forces acting in the system are determined by the viscous flow of the body corresponding to its yield limit. Above the elasticity limit of the body, we observe the formation of a bistable state of the system caused by changes in the controlling parameters and lag effects and leading to its macroscopic acoustic activity. I. N. Frantsevich Institute for Problems in Material Science, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 16–27, July–August, 1998.     

Localized shear in sheet materials

Procedures and results of numerical simulations and experimental investigations of sheet materials under localized plastic deformation in shear are presented. Under dynamic loading these materials are considered to be viscoelastoplastic solids. Localized deformation and stress-strain distributions resulting from plastic shear are examined as a one-dimensional problem with account for nonlinear viscosity, damage, and temperature effects. Mild steel and high-strength aluminum alloy strips were tested under multiple impact loading with a small strain increment per impact (which corresponds to isothermal loading with sufficient accuracy). The experimental relations of localized shear deformation under such loading allow one to make the conclusion of a prevailing stress concentration effect on the kinetics of localized shear at the edge of the strip. Institute of Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 5, pp. 53–63, September–October, 1999.     

Devices for monitoring the thermal state of the object “enclosure”

The design of heat flow and temperature metering equipment used at the Chernobyl Atomic Power Station for heat and temperature diagnosis of the state of the damaged reactor is described. Deceased. Institute for Problems of Energy Conservation, Academy of Sciences of Ukraine, Kiev. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 2, pp. 255–260, March–April, 1996.     

Numerical analysis of laminated anisotropic shells and plates based on the iterative shear theory

We consider a problem of bending of laminated anisotropic smooth shells and plates. On the basis of the method of iterations, we construct new, more precise mathematical models of the stress-strain state with different degrees of accuracy which take into account transverse shear strains. The properties of the developed models are studied by analyzing the problem of bending of rectangular diagonally reinforced laminated plates. It is shown that the application of the iterative approach to the construction of these models enables one to obtain results which converge to the three-dimensional solution of the problem as the degree of approximation of the model increases. Ukrainian Transport University, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 100 – 106, January – February, 1998.     

Special features of dynamic fracture of brittle materials in the mode of ultimate fracture velocities

Based on the model of spherical cavity expansion in brittle materials, which involves the concept of ultimate fracture velocities, we consider a stress-strain state in the elastic precursor zone and in the region of material broken by radial cracks. We have noted the mechanical effects of dynamic overload and fracture retardation, which arise within this model. Institute of Problems of Materials Science, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 2, pp. 20–26, March–April, 2000.     

Thermomechanical behavior of a viscoelastic finite circular cylinder under harmonic deformations

A coupled thermomechanical behavior of a finite viscoelastic cylinder under harmonic kinematic excitation at its ends is investigated. The method of superposition is utilized to determine the stress-strain state of the cylinder. A refined asymptotic technique is developed to find the stress-strain state at each point of the body including the corner. Stiffness characteristics are examined over a broad range of cylinder-geometry parameters. By use of known stress components the function for the dissipation rate is constructed and the temperature field of vibration heating is calculated by solving the appropriate heat-conduction boundary-value problem. For the case of strong temperature dependence of loss modulus the phenomenon of thermal instability is examined.     

Numerical simulation of temperature fields in elastomeric structures with cracks on the basis of singular finite elements

We describe a method used for the investigation of temperature fields of dissipative heating in elastomeric structures with cracks. Determining relations are constructed on the basis of a moment scheme of finite elements with application of singular quadratic elements. The -type singularities of the stress and strain fields at the crack tip are simulated by shifting the intermediate nodes by a quarter of the length of the side toward the crack tip in the basic coordinate system, while the functions of shape remain unchanged in the process of construction of the stiffness matrix. As an example, we study the problem of determination of temperature fields in continuous cylindrical, trough-shaped, and rectangular shock absorbers of complex geometry with cracks. The proposed method is realized in the form of a software complex for personal computers called KODETOM. Lugansk Agricultural Institute, Lugansk, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 83–93, May–June, 1998.     

Residual stress-strain state of the collector assembly of a steam generator in the process of press-fitting of heat-exchange pipes

The influence technological heredity connected with the manufacturing process on the strength and service life of the assembly of joints of the collector and heat exchange pipes of a steam generator proves to be one of the main causes of premature failures of steam generators of water-cooled reactors of nuclear power plants. We present the results of a numerical simulation of the process of press-fitting of heat-exchange pipes in the collector. We determine the residual stress-strain state of the collector assembly depending on the basic technological parameters of press-fitting (the initial gap between the pipe and the collector, the pressure of hydraulic press-fitting, and the boundaries of the region of application of pressure) and strength characteristics of the materials of the collector and pipes. We also estimate the influence of the additional mechanical flaring of pipes and redistribution of local stresses in the course of consecutive hydraulic press-fitting on the level of residual stresses in the collector assembly. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 2, pp. 66 – 86, March – April, 1998.     

Gas flow through a porous heat-releasing medium with allowance for the temperature dependence of gas viscosity

The gas flow through a porous heat-releasing medium is considered. It has been noted that account for the temperature dependence of the gas viscosity strongly influences the solution: the gas flow rate markedly decreases and a stronger heating occurs. Analysis of the flow of a gas with a temperature-dependent viscosity by the Sutherland formula has revealed two steady-state cooling regimes — stable and unstable ones. It has been shown that the possibility of the steady-state regime is determined not only by the problem parameters but by the initial conditions as well. The transient process from the state of rest in the absence of heat release to the state of the regime of induced filtration upon instantaneous switching-on of heat input is described. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 1, pp. 35–40, January–February, 2006.     

Analysis of boundary-value problems describing the non-isothermal processes of elastoplastic deformation taking into account the loading history

We discuss the theory and approximate methods for solving boundary-value problems of thermoplasticity in a quasi-static formulation when the process of non-isothermal elastoplastic deformation of a body is a sequence of equilibrium states. In this case, the stress-strain state depends on the loading history, and the process of inelastic deformation is to be observed over the whole time interval being studied. The boundary-value problem is stated as a non-linear operator equation in the Hilbertian space. The conditions that provide the existence, uniqueness and continuous dependence of the generalized solution on the applied loads and initial strains are defined. A convergence of the methods of elastic solutions and variable elastic parameters is studied to solve the boundary-value problems describing the non-isothermal processes of active loading taking into account the initial strains dependent on the deformation history and heating. __________ Translated from Problemy Prochnosti, No. 1, pp. 69–99, January–February, 2006.     

Stressed state of a thermosensitive plate in a central-symmetric temperature field

The problem of thermoelasticity for a thin thermosensitive plate placed in a central-symmetric temperature field is reduced by the perturbation method to a recurrent sequence of boundary-value problems for differential equations with constant coefficients. On this basis, we obtain solutions for the cases of load-free circular washer, infinite plate with circular hole, circular disk, and infinite plate. The stress-strain state of an infinite plate containing a circular hole is investigated. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 2, pp. 5–12, March–April, 2006.     

Basic relations of the theory of nonlinear dynamic deformation of high-strength polymer films

We present basic relations of the theory of nonlinear dynamic deformation of rigid (high-strength) polymeric films. On the basis of the experimental results, we formulate the determining relations for the elastic and plastic stages of deformation. We introduce a measure of the stress-strain state and obtain the equations of motion for arbitrary curvilinear orthogonal coordinates in the case of large displacements and low strains and squares of the angles of rotation. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 6, pp. 127–133, November–December, 1999.     

Dynamics of uniaxial tension of a viscoelastic strain-hardening body in a system with one degree of freedom. Part 2. Action of external forces

We analyze the motion of a mechanical dissipative system containing a viscoelastic strain-hardening body with one degree of freedom under the action of an external tensile force depending on its controlling parameters and initial loading conditions. We construct periodic and aperiodic solutions of a nonautonomous third-order dynamical system taking into account transient processes of motion from the initial state. It is shown that the transient process of motion of the system is realized either as forced damped oscillations responsible for its acoustic activity or as an aperiodic process of damping. We also consider transient dynamic processes in a viscoelastic Maxwell body subjected to static loading in the case where strain hardening is absent. Frantsevich Institute for Problems in Materials Science, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 5, pp. 12–26, September–October, 1998.     

Database of physicomechanical properties of materials and its use in applied software packages

We describe a database of physicomechanical properties of materials with the possibility of automatic entry of the relevant data in applied software packages designed for the analysis of stress-strain states of structural members. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 90–94, July–August, 1997.