A computational model to determine the residual life of a long steam turbine blade containing a short corrosion-fatigue defect (crack) is proposed. The blade is subjected to longitudinal tensile loading due to centrifugal force and cyclic bending in the plane of the disk. The computational model is formulated in terms of the crack tip opening displacement δ, which makes it possible to study microdefects in quasi-plastic materials. Based on available experimental data and the proposed analytical transformation, fatigue fracture kinetics diagrams for 20Kh13 steel are constructed in the da/dN ~ δt coordinate system. The residual life of a 20Kh13 steel blade is calculated. The influence of bending stresses caused by variable steam pressure at the nozzle exit, as well as the localization and initial size of the crack, on the residual life of the blade is evaluated.

A computational model has been developed to assess the effect of material degradation on the residual life of a long steam turbine blade containing a corrosion-fatigue crack, subjected to axial tensile loading due to centrifugal forces and cyclic bending in the disk plane caused by variations in the steam outlet pressure from the nozzles. Analytical relationships describing the time variation of degradation parameters of 20Kh13 steel under corrosion-fatigue loading conditions are proposed. Its influence on the residual life of the blade made of 20Kh13 steel is evaluated.

Using the energy approach, a mathematical model is developed to study the kinetics and determine the period of subcritical growth of a crack system in a plate under the influence of corrosive environment and a maneuverable loading mode. The mathematical model is a differential equation with initial and boundary conditions which describe the rate and direction of crack propagation. The model was applied to determine the residual lifetime of a plate made of steel St3 with a two-periodic system of cracks under maneuverable loading and corrosive-active environment.

A computational model is constructed to study the effect of operational material degradation on the residual life of a composite bimetallic plate at high temperature and under long-term static loading. The model is based on a differential equation, which describes the growth of a high-temperature creep crack and contains the parameters of material degradation. The residual life of the composite plate is estimated in the case when it consists of 12Kh1MF steel and IN-100 alloy.

A computational model is proposed to determine the residual life of a composite bimetallic plate made of semi-infinite plates of 15Kh2MFA and 321 steels with a rectilinear crack. The plate is statically tensioned at a high temperature and under the influence of a hydrogen-containing environment by uniformly distributed forces perpendicular to the line of its placement. The model is based on the energy approach about the balance of external forces and the resulting internal energies. This model is implemented numerically. Graphical dependences of the change in the residual service life of a plate on the size of the initial crack and the influence of a hydrogen-containing environment were constructed.

Using the energy approach, a mathematical model is developed to study the kinetics and determine the period of subcritical growth of a system of cracks in a plate under the influence of a corrosive environment and a maneuver loading mode. The mathematical model is a differential equations with initial and boundary conditions, which describe the rate and direction of crack propagation. The model was applied to determine the residual life of a plate made of steel St3 with a two-periodic system of cracks under maneuver loading and corrosive-active environment.

A complex method of applying acoustic emission (AE) and the previously developed energy approach to determine the residual life of thin-walled structural elements under conditions of long-term static load, corrosive environment effect, and operational degradation of materials is developed. The method is based on the first law of thermodynamics of the balance of energy components and the work of external forces, as well as their rates of change for an elementary jump of crack propagation. The hypothesis of a linear relationship between the dimensions of the area of the active crack and the number of acoustic emission pulses released at the same time is assumed. The change in the characteristics of the oil and gas pipeline material during its operational degradation is mathematically modeled by a linear time dependence. The above-formulated problem of determining the residual life of a thin-walled structural element was solved using the energy approach and was reduced to a differential equation with initial and final conditions. In the mathematical problem obtained in this way, two parameters are unknown: the size of the initial plane crack and the loading parameter of the material near it. These parameters were determined as follows. With the help of the AE device during the given time (150 h), the number of AE pulses and the rate of their counting were recorded. These values were introduced into the established formulas for determining the area of the initial crack and the parameter of loading of the material in its vicinity. To demonstrate the application of this complex method, a numerical experiment was performed, and the residual life of an X70 steel plate was determined.

Using the energy approach, a calculation model was built to determine the period of subcritical growth of a system of cracks in metal plates, subjected to long-term static tension and local electrochemical corrosion. The effect of a corrosive environment on the residual life of a plate with a system of periodic and doubly periodic cracks was evaluated.

Based on the energy approach previously developed by the authors, the problem of determining the residual life of an oil pipeline pipe with a surface semi-elliptical microcrack, into which the soil corrosive medium penetrates, is solved. A turbulent flow of oil moves along such a pipe, which causes two-frequency loading of its wall. Microdefects and the plastic material of the pipe, which degrades during crack propagation, are considered. Therefore, the solution to the problem, using the energy approach, is reduced to a nonlinear differential equation for the crack opening function at its pre-fracture zone with variable coefficients. The equation together with the initial and final conditions (crack opening on the inner surface of the pipe and its depressurization) is a mathematical model for determining the residual life of the pipe. The crack opening function is found approximately using the method of equivalent stress states and the limit interpolation method developed earlier by the authors. The dependences of the residual life of the oil pipeline pipe made of X70 steel, considering its material’s degradation, are obtained.

A method for estimating the residual life of X70 steel pipe of an oil pipeline with an external surface semi-elliptical crack, in which there is a laminar flow of oil under a pressure of 12 MPa, and a soil corrosive medium penetrates the crack, is proposed. The residual life of such a pipe after 33 years of operation, when corrosion-hydrogen degradation of its material takes place, was studied. Based on the experimental data on the degradation of X70 steel, known in the literature, an approximate basic diagram of the corrosion-mechanical crack growth in such a material was constructed. The energy approach previously formulated by the authors for determining the residual life of an oil pipeline pipe with a corrosion crack is applied to the new problem obtained in this way, when the basic diagram of such crack growth includes the simultaneous degradation of X70 steel. Graphical dependences of the residual life of the pipe on the initial size of the crack based on the simultaneous degradation of its material as well as for the cases of the reserve pipe and the pipe operated for 33 years are constructed and results are compared.

An acoustic-emission method for determining the residual life of power equipment with hightemperature creep cracks under long-term static tensile load has been developed. This method is based on the method, previously proposed by the authors, of constructing a reference acoustic-kinetic diagram of the propagation of a high-temperature creep crack in the same material as the object under study, as well as a scheme of a reference analytical acoustic pattern (acousogram) during crack propagation. The essence of the method is as follows. It is believed that the object fracture takes place by the propagation of already existing plain cracks in it, near which there are normal tensile stresses. It is proposed to determine the initial area of the crack and the load of the object based on the parameters of the acousogram recorded during crack propagation in the investigated object. The numerical experiment was conducted to demonstrate the application of this method.

Using the energy approach formulated earlier by the authors, a mathematical model was constructed, which in turn is the basis of the calculation method for predicting the residual life time of the rectification column for production of ethylene under the wind load and atmospheric corrosion. It should be noted that wind load is shunting in nature with constant pressure on the column and frequent gusts. There is an external surface corrosion-mechanical crack in the circular weld, by which the column is attached to the base. The corrosive environment penetrates into this crack. Such a corrosive environment together with the shunting wind load intensifies crack propagation to the size, which causes failure of the column. Using the energy approach, this problem is reduced to special differential equations with special delta functions, which are solved approximately for a large number of wind gusts. Using the energy approach the dependence of the 09G2C steel column residual life time on the number of wind gusts, was investigated.

An acoustic-emission model of local fracture (crack propagation) of the material is constructed. Based on this, a method of determining the residual life of thin-walled structural elements under the action of long-term static load and corrosive environment has been developed. The size of the crack and the stress in its plane are determined by the parameters of the acoustogram written from the structural element during crack propagation. To demonstrate the application of this method, a numerical experiment is conducted and the residual life of the plate is determined.

The accuracy of the damage and the outcome of the battle depend on the durable wear resistance of the inner surface of the artillery barrels. When fired, there is close contact between the surface of the barrel and the rings of softer metal on the projectile (this is for the tightness of the system), which leads to their active abrasion. True, the softer surfaces of the rings on the projectile wear more, but with such rapid mutual movement of the surfaces, the harder materials of the barrel also wear. As a result, the tightness of the powder gases is violated and, accordingly, the power of the shot and the flight range of the projectile, as well as the amplitude of the oscillation of the projectile during its passage through the barrel increases. This in turn affects the accuracy of hitting the target, especially at long distances. For close combat, this is not a big problem, but long-range artillery systems are most important now. In this regard, the purpose of this research is to develop a technology for manufacturing a cannon barrel with the most wear-resistant inner surface. At the same time, a brief review of artillery systems, which are currently used mainly in the Russian-Ukrainian war, is made. The scheme of the manufacturing technology of rifled tank barrels with an increased resource of aiming lesions is described. The methodology is based on the technology of their surface hardening with high-frequency currents and grinding of microcracks, which appear as a result, developed by the authors. The main factors that ensure a high resource of barrels according to the technology are their high heat resistance and wear resistance. Heat resistance is achieved by optimizing the material on the samples, wear resistance by optimizing the parameters of the surface hardening technology of the inner surface of the barrel. The method of calculating the survivability of the barrel is given, when after hardening and grinding of the barrel, a micro crack remained on its inner surface.

We propose a three-dimensional mathematical model of hydrogen diffusion in a polycrystalline body taking into account the heterogeneity of diffusion parameters and the solubility of hydrogen in the grain body and on the grain boundaries. The obtained solution is verified for an iron bicrystal. It is shown that the model of grain-boundary diffusion of hydrogen enables one to determine a characteristic value of hydrogen concentration corresponding to changes in the mechanism of deformation.

We propose a computational model for the determination of the residual service life of a torsion bar (cylinder) subjected to long-term twisting under the action of corrosive media. The model is based on the deduced differential equation for the kinetics of propagation of a stress-corrosion crack from its initial size to the ultimate size. We determine the residual service life of a torsion bar made of 45KhN2МFА steel and containing a semielliptic crack whose plane is directed at an angle of 45° to its axis under the action of long-term twisting.

We formulate basic equations of the mathematical model, which enable us to determine the influence of hydrogen and mechanical loading on the plastic deformation of the metal. It is shown that hydrogen may increase or decrease the velocity of dislocations in pure α -Fe depending on its concentration, temperature, and applied loads. For low concentrations (up to 2–3 ppm), hydrogen intensifies the motion of dislocations, thus increasing the plastic strain rate.

We present a survey of the results of theoretical investigations of the method of acoustic emission used for the determination of the limit equilibrium of materials with cracks, their delayed fracture (initiation and propagation of cracks), and the residual service life of structural elements intended for long-term operation. At the same time, we develop computational models for the detection, by the acoustic-emission method, of crack-like defects and volumetric damage to the materials. We also propose criteria for the mechanisms of their fracture and acoustic-emission procedures aimed at the construction of the kinetic diagrams of delayed growth of creep cracks.

Based on the energy approach formulated earlier by the authors, the calculation model for determining the durability of a fiber-reinforced concrete beam under long-term pure bending and local creep was developed. The model relied on the first law of thermodynamics regarding the energy balance and the balance of rates of energy variations in the fiber-reinforced concrete beam with initial volumetric damage after such loading. The following provisions and assumptions were introduced. Matrix and fiber materials were homogeneous and isotropic. The process of cracking in concrete occurred after the stresses attained the strength value of concrete. Opening of the generated microcracks and pull-out of fibers from concrete was treated as the main mechanism of its creep. The tensile diagram of fiber concrete was taken as piecewise linear. For simplicity of calculations, the area of the tensile diagram corresponding to the second stage of deformation was approximately represented by a straight line, similar to the compression case. During long-term bending of the beam element, the loss of its carrying ability was determined mainly by the stress-strain state of the tensile zone. Its rheological characteristics in the first approximation were assumed to be equal to the compressed ones. Fibers (of the same circular section and length) in the tensile zone were evenly distributed in all directions and were subjected to tension only. There was a complete adhesion between the fibers and the concrete, so their strains were identical. To improve the computation efficience, we used the plane section hypothesis, simplified models of fiberreinforced concrete deformation under tension, compression, and bending, as well as the creep condition of its creep at fracture (loss of performance properties of the fiber-reinforced concrete beam). The model feasibility was proved by the durability assessment of a real fiber-reinforced concrete beam with specified characteristics from literature.

We propose a method for the determination of the residual service life of wide-coverage spraying booms of field sprinklers with regard for the maneuvering mode of their loading and the action of corrosive media. This method is based on the energy approach developed earlier, the computational models of propagation of corrosion cracks under static and cyclic loads, and the scheme of the maneuvering loading mode. In the realization of the proposed model, we use a boom made of St.3 steel.