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|Kushnir R. M. and Popovych V. S. Stress state of a thermosensitive plate in a central symmetric temperature field
SUMMARY. The thermoelasticity problem for a thin thermosensitive plate in a central symmetric temperature field is reduced to a recurrent sequence of boundary-value problems using the perturbation method. The differential equations of these problems have constant coefficients. On this basis the solutions are obtained for a load-free circular disk, an infinite plate with a circular hole, a disk and an infinite plate. The stress-strain state of an infinite plate with a circular hole is investigated.
|Gorynin I. V. and Timofieiev B. T. Ageing of the nuclear power plant equipment materials after designed service life
SUMMARY. The results of the investigation of thermal ageing effect on mechanical properties of the base metal and welded joints metal of the elements of equipment and pipes of the first circuit of NPP with the WMR and HTGR reactors during durable service life are generalized. The comparison of the initial properties of these materials after 105 and 2Ч105 h operation time showed that the changes are insignificant and the mechanical characteristics after 30 year operation are not lower than that required by standard ПНAE Г-7-002-86 for the widely used grades of steels and ПНАЕ Г-7-010-89 for the welds metal.
|Torskyi A. R., Chaplia Ye. Ya., and Chernukha O. Yu. Diffusion decaying admixtures
in materials with random inclusions
SUMMARY. Admixture diffusion is investigated in a layer of a nonhomogeneous material with the account of random spherecal inclusions, modelling, for example, avalanche fuel-bearing masses in atomic power plants. A contact initial-boundary value problem of diffusion is reduced to an initial-boundary value problem of mass transfer in the whole body by the theory of generalized functions. The equivalent integro-differential equation is formulated. Its solution is obtained by the method of successive iterations in the form of integral Neumann series. Convergence of the series as well as the solution existence theorem is proved. The approximate formula for calculation of the admixture concentration averaged over the ensemble of phase configurations is found, and numerical analysis is carried out. The influence of material characteristics on the behaviour and concentration of admixtures in a body of random nonhomogeneous structure is shown. If diffusion coefficient in inclusions is less then that in a matrix the increase of the averaged concentration in the layer area and vice versa is observed. Account of the admixture particle decay leads to the several-fold decrease of the averaged concentration.
|Krasovskyi A. Ya. About “local approach” to structural materials brittle fracture
SUMMARY. The principles and sources of the important direction in fracture mechanics – so-called “local approach” to the problem of the materials fracture are considered. This approach provides the possibility to describe the material crack growth resistance using their conventional mechanical properties as well as opens the door to determination of the limiting state of structural elements. As the first example of such approach application, the general features of two-parametric Km-model related with the “global”, KIс, and “local”, rс and sс, parameters via the yield conditions on the contour of the small plastic zone at the crack tip are presented. This approach has been significantly developed in the last decades. It has been applied in the field of quasi-brittle and ductile failures. The main fundamental statements are given which were substantiated and further developed in the last decades.
|Kit H. S. and Sushko O. P. Thermoelastic state of a semispace with a perpendicular
to its boundary thermoactive elliptical crack
SUMMARY. Using the boundary integral equation method, the problem of stationary heat conduction and thermoelasticity for a semi-infinite body with an elliptical crack perpendicular to its boundary is solved. The temperature is given on the crack surface.The body boundary is load-free and is thermally insulated or is maintained at zero temperature. The influence of lying depth of the crack and its location on the stress intensity factor is studied for the given constant temperature on it.
|Mirsalimov V. M. Cracks with ligaments between edges in a bushing of a friction pair
SUMMARY. The problem about the contact deformation of the bushing of a frictional pair is considered. On the bushing friction surface rectilinear cracks with end zones in which crack edges interact are located. During reciprocal motion of a plunger the material of the bushing fails due to contact interaction. The boundary problem about equilibrium of the bushing of a friction pair with cracks, having connections between faces, is reduced to the solution of the system of nonlinear singular integrodifferential equations with Cauchy kernels. From the solution of this system normal and tangential stresses in connections are found. The condition of limiting equilibrium of the crack is formulated on the basis of criterion of a critical connection elongation.
|Andreikiv O. Ye. and Sas N. B. Fracture mechanics of metal plates under
SUMMARY. A calculation model for evaluation of subcritical crack propagation under high-temperature creep in metallic plates is proposed. The model is based on the first low of thermodynamics on energy balance and the balance of energy change velocity in a metallic plate, containing a macrocrack and subjected to long-term static loading tension under high-temperature field effect, thus providing the stable creep in the process zone near the crack tip. On the basis of above mentioned the equation for evaluation of the macrocrack growth under high-temperature creep is obtained. These equations with original and final conditions form the mathematical model for determining the subcritical crack growth period under high-temperature creep in metallic plates. The correctness of this model is confirmed by experimental data.
|Sulym H. T., and Kundrat M. M. Limit equilibrium and fracture of an orthotropic body with thin rigid inclusions
SUMMARY. Limiting equilibrium and fracture of an orthotropic body with a linear inclusion under tension at infinity along the inclusion axis is investigated. Localized process zones (weaken contact) develop along the plate-inclusion boundary from its ends to the central part. Analytical solution of the problem by means of complex potentials is obtained. The influence of load and orthotropic matrix on development of the process zones, distribution of contact stresses, axial forces in the inclusion, character of fracture in a composition are investigated. Limiting loads of possible inclusion lamination or its rupture are established. Examples of their calculation are presented.
|Chekurin V. F. and Pokhmurska H. V. A field of residual stresses in a cracked coating
SUMMARY. A body with a coating deposited on its plane surface is considered. The known uniaxial homogeneous tensile stresses act in this body. A field of residual stresses that would act in the coating after initiation of a long plane crack perpendicular to the direction of tensile stresses and the body surface is investigated. A problem is considered in the plane strain formulation – the stress field in the section perpendicular to the crack plane and surface coating is studied. Two cases are considered – when a crack passes through the whole coating thickness and a case of non-through crack on the continuation of which the plastic zone exists. The numerical investigations have been conducted that enable the evaluation of the mechanisms of coating fracture after the crack initiation.
|Yushchenko K. A. and Derlomenko V. V. Weldability and change of physicomechanical properties of welded joints
SUMMARY. The new definition of weldability takes into account the dependence of the last one on the degree of material degradation and can be evaluated as an integrated indicator. Examples of degradation of some materials characterising their weldability are given. Preconditions for development of a modern concept of weldability in terms of its control are considered.
|Kyrian V. I. and Shonin V. A. New representation of limit stress diagrams for fatigue calculations of aluminium structures
SUMMARY. A new analytic representation of limit stress diagrams of constant fatigue life is proposed. These are calculated using limited experimental data obtained from fatigue tests of smooth specimens of welded joint metal of aluminum alloys. When determining the “hot spot stress” state such diagrams allow to calculate fatigue properties of aluminum constructions taking into account stress concentration, level and character of residual stress distribution, misalignment in joining zone etc.
|Osadchuk V. A., Banakhevych Yu. V., and Ivanchuk O. O. Calculation- experimental diagnostics of stresses in main pipelines near circular welds
SUMMARY. Using the calculation-experimental method, based on solution of inverse problems of the theory of a shell with residual strains, and utilizing the experimental data obtained by nondestructive test methods, the distribution of residual stresses near the circumferential weld in the main pipelines is defined and analyzed, the non-uniformity of their distribution under the measuring devices is considered. With the help of these devices the averaged characteristics of the stress state are defined experimentally with regard to the influence of the structural changes in the heat effected zone.
|Toribio J. and Kharin V. Effect of residual stress-strain profiles on hydrogen induced fracture of prestressing steel wires|
|Nakonieczny A. Fatigue fracture of nitride layers|
|Klapkiv M. D., Povstiana N. Yu., and Nykyforchyn H. M. Creation of conversive oxide ceramic coatings on zirconium and titanium alloys
SUMMARY. Possibilities of the surface strengthening by conversion oxide-ceramic coatings on zirconium and titanium alloys are considered. Coatings are obtained by a plasmoelectrolyte treatment method in alkaline solutions. It was established that plasma temperature in discharge spark channels attains (6...9) Ч 103 K. The coating thickness was 100...120 and 30...40 μm, microhardness ~800 and ~1000 MPa for zirconium and titanium alloys respectively. The functional properties of coatings depend on the synthesis regimes: electrolyte content, anodic and cathodic current densities and time of treatment. Coatings thickness, microhardness, wear resistance at dry friction and cavitation, fatigue strength and corrosion resistance were evaluated. It was established that the applied treatment provides high wear and corrosion resistance of investigated alloys at insignificant decrease of fatigue strength.
Ihor Vasyliovych Gorynin (to the 80th birthday)
Rostyslav Melekhov (an obituary notice)
|Stanislav Kocanda (an obituary notice)|