The residual life of the runners of hydraulic turbines in the presence of operational defects is estimated. The main problems of the operation of hydraulic turbines associated with technological defects and exhaustion of the standard resource are described. The main requirements for initial data to be used in estimation of the residual resource and the requirements for predicting the residual resource of runners based on the results of surveys and analysis of their technical condition are specified. We have classified and briefly described the applied approaches and techniques used in estimation of the residual resource. The main damaging factors affecting the residual life of the runners are revealed: deformation aging of the metal, cavitation, corrosion and fatigue damage to the elements of runners. The most characteristic defects are divided into three groups: zones of cavitation erosion; corrosion-fatigue cracks; and weld defects. Particular attention is paid to corrosion-fatigue cracks identified using flaw detection. The mechanism of crack formation and the most probable location of the cracks in the runner are shown. Statistical data on the number of cracks at the onset of the runner operation and at the time of shutdown maintenance are presented. The main statistical parameters of the sample and the parameters of crack size distributions including the distribution law are determined. The distribution law is exponential for the crack length parameter; whereas for the crack opening width it is log-normal. The revealed multidirectional cracks are located at the surface, subsurface or inner layer of the metal. They arise from operational defects (ulcers, craters, undercuts or delamination) and grow during operation of the turbine units. We also present the design schemes of elements with cracks used for quantification of resources according to the criteria of fracture mechanics. The results of calculations for static and dynamic crack resistance are presented as the dependence of stress intensity factors on the crack size. The levels of the total accumulated damage to the runners, the values of the residual life at the stage of crack nucleation and development were determined for 11 hydraulic units in the «start-stop» and «working» cycles. The main conclusion is that the total operating time of the hydraulic turbine runners significantly exceeds the standard operating life, while the residual resource is insufficient for a further period of long-term operation.

Представлены направления основных исследований, выполненных коллективом авторов в период с 1985 г. по настоящее время, результаты которых получили отражение в издательском проекте научных, научно-технических и прикладных разработок “Конструкционная прочность. Ресурс. Механика разрушения. Безопасность технических систем”. В рамках проекта опубликовано десять коллективных монографий. В обзорной форме отражены результаты исследований предельных состояний, характеристик трещиностойкости конструкционных материалов, композитных конструкций космических аппаратов, разработки в области создания машин и конструкций для условий Сибири и Арктики, приведены примеры результатов диагностики технического состояния и анализа причин аварий сложных технических систем. Отмечена приоритетная роль математического моделирования в решении обозначенных задач, особенно при анализе напряженно-деформированных состояний The article presents the directions of the main research carried out by a team of authors in the period since 1985. The results of the research were reflected in the framework of the publishing project of scientific, scientific, technical and applied developments “Structural strength. Resource. Destruction mechanics. Safety of technical systems”. Ten collective monographs have been published within the framework of the project. The review form reflects the results for studies of limit states, crack resistance characteristics of structural materials, composite structures of spacecraft, developments in the field of creating machines and structures for the conditions of Siberia and the Arctic. Examples of the results of diagnostics of the technical condition and analysis of the causes of accidents of complex technical systems are given. The priority role of mathematical modelling in solving the indicated problems, especially in terms of the analysis of stress-strain states, is anticipated

The technologies and results of an experimental determination of residual stresses in the impeller blades of a hydraulic unit of the Krasnoyarsk hydroelectric power plant obtained through technical diagnostics beyond the projected periods of use are presented. The investigations of the residual stresses were performed by strain measurement with excision of templates and the optical method of speckle interferometry. Factual values of the components of the residual stresses in two zones of the blade with nonuniform stress fields were obtained.

The results of unique experimental studies of the strength and service life of a metal-composite high-pressure tank are presented. The study is aimed at analyzing the fracture mechanisms and evaluating the strength characteristics of the structure. The technique included tests of full-scale samples of the tank for durability under short-term static, long-term static, and cyclic loading with internal pneumatic pressure. The generalized test results and data of visual measurements, instrumental and acoustic-emission control of deformation processes, accumulation of damage, and destruction of full-scale tank samples are presented. The strength and the stiffness of the structure exposed to internal pneumatic pressure are analyzed. The types of limiting states of the tanks are established experimentally. Variation in the stress-strain state of the tank under cyclic and prolonged static loading is considered. The specific features of the destruction mechanism of the metal-composite tank are determined with allowance for the role of the metal liner strain. The calculated and experimental estimates of the energy potential of destruction and the size of the area affected by destruction of the tank are presented. Analysis of the test results show that the tank has high strength and resource characteristics that meet the requirements of the design documentation. The experimental results are in good agreement with the results of the numerical calculations and analysis of the stress-strain state and destruction mechanisms of the metal-composite tank.

— The failure criteria and limit states for thin-walled pressure vessels are analyzed taking into account the influence of plastic deformations. The introduction describes the main problems in operation of thin-walled vessels working under internal excess pressure associated with technological defectiveness and reduction of the residual life. Typical technological and operational defects in welded joints of vessels and statistical data on their number and types are presented. The share of welding defects is 62% of the total number of defects, and the share of remaining types of defects is significantly less. Histograms of the dimensions of welding defects are drawn, and the distribution laws are determined: the length of undercuts is described by a lognormal distribution law, whereas the depth of undercuts is described by a normal distribution law. Further, the limiting states and fracture criteria of vessels with defects and cracks under the conditions of elastoplastic deformation of material are indicated. The advantages of using the generalized equations of the form of J -curves are shown for calculation of the cracking resistance. A formula is given for calculating the J -curves that associate the dimensionless J -integral with the dimensionless load. The stress-strain state of a thin-walled vessel with a surface half-elliptical crack and an internal elliptical crack is analyzed in a volumetric setting. The peculiarities of the stress and strain fields in the local region of the crack zone under elastoplastic deformation are investigated. For the vessel model with a surface half-elliptical crack and an internal elliptical crack under elastoplastic deformation, the energy criterion of fracture mechanics, the J -integral, is calculated, and the results of calculations are presented. The results are presented in the form of graphs of the dimensionless J -integral versus the geometrical dimensions of the vessel and crack. The equations of J -curves are obtained and the limit load for thin-walled vessels is determined which depends on geometrical dimensions, loading parameters, strength properties of the material, and characteristics of cracking resistance and deformation. From the J -curves and the deformation curve, a formula is derived for determining the dependence of the limit load on the crack size, loading parameters, and characteristics of the material. Using this formula, the dependences of the limiting pressure of the vessel under elastoplastic deformations on the ratio of crack length a to vessel wall thickness S ( a / S ) is plotted for surface and internal cracks with different ratios R / S ( R is the shell radius) and J c which allow estimating the limiting pressure levels of the safe operation of thin-walled vessels.

The analysis of failure criteria and limit states for thin-wall pressure vessels is carried out, taking into account the influence of plastic deformations. The introduction describes the main problems of operation of thin-walled vessels operating under internal excess pressure, associated with technological defectiveness and reduction of the residual life. Typical technological and operational defects in welded joints of vessels and statistical data on their number and types are presented, their grouping and statistical processing are carried out. The share of welding defects was 62 % of the total number of defects, the remaining types of defects are much smaller. The histograms of the dimensions of welding defects were constructed and the distribution laws were determined: the length of the cuts was described by the lognormal distribution law, the depth by the normal distribution law. Further, the limiting states and criteria for the destruction of vessels in the presence of defects and cracks in the conditions of elastoplastic deformation of the material are indicated. The advantages of using generalized equations of the form «J-curves» when calculating for fracture toughness are shown. A formula is given for the calculation of «J-curves» connecting a dimensionless J-integral with a dimensionless load. An analysis is made of the stress-strain state of a thin-walled vessel with a external half-elliptical and internal elliptical cracks, in a volumetric setting. The peculiarities of the stress and strain fields in the local region of the crack zone under elastoplastic deformation were investigated. The accountings are performed and the results of evaluation of the fracture mechanics energy criterion — J-integral for vessel model with the external half-elliptical and internal elliptical cracks in elastic-plastic deformation — are presented. The results are presented as graphs of the dimensionless J-integral dependency on the geometrical sizes of the vessel and crack. The equations of «J-curve» were obtained and the ultimate load for thin-wall pressure vessels were determined. That ultimate load depends on the geometrical dimensions, loading parameters, structural behaviors of material, the characteristics of crack strength and deformation. On the «J-curves» and the deformation curve, a formula is obtained for determining the dependence of the ultimate load on the crack size, loading parameters and material characteristics. Using this formula, we plotted the dependences of the vessel’s limiting pressure for elastoplastic deformations on the ratio a/S for surface and internal cracks for different ratios R/S and Jc, which allow estimating the levels of limiting pressure for the safe operation of thin-walled vessels.