539.4:621.165 I. I. Melezhyk, and T. V. ProtasovaThe thermostressed state and crack growth resistance of rotors are analyzed for various operating conditions using the procedures developed for their calculation. The kinetics of transverse cracks under high-cycle loading is considered.The majority of power-generating units of Ukrainian nuclear power plants (NPP) that generate about 52% of electric power are operating for than 20 years. The specified life of two power units of the Rivnenska NPP (above 30 years) will be exhausted in 2010-2011, and that of one power unit of the Yuzhno-Ukrainska NPP in 2012. In this connection, their equipment, including turbine plants, requires a comprehensive approach to evaluate the technical state, to assess the lifetime and to extend it. In contrast to high-temperature steam turbines, the material creep in NPP moist steam turbines is absent. Therefore, for assessing the damage in rotor elements it is important to determine the influence of low-cycle fatigue on the serviceability of the structure. As evidenced by operational experience, erosion-corrosion processes are decisive for NPP turbines.The most highly stressed areas in turbine rotors under varying modes of operation were determined with the help of boundary conditions of heat exchange for restricted schedules of cold and hot starts of the turbo unit and scheduled unloading, the calculations of unsteady thermal fields and the thermal stress state of rotors using the finite element method [1]. In so doing, transient problems on heat conductance and thermal stress levels were solved using the same finite element mesh [2]. The investigations of stress-strain state of rotors during a hot start (HS) of the turbine unit included the steady mode of operation, a scheduled outage with no loss of vacuum, and cooling for 8 h. All rotors were double flow rotors with the symmetry plane located in the center, therefore, only their symmetrical halves were considered.In a high-pressure rotor (HPR) of the NPP turbine (model K-100-60/1500), the maximum stress intensity is attained during a hot start of the turbine unit after its shutdown for 8 h and is 195 MPa in gaining 400 MW of power. The isothermal lines and stress intensity distribution corresponding to this case are presented in Fig. 1. The maximum stress intensity is attained on the internal surface of the rotor beneath the 5th stage and in disc grooves (Fig. 1b).Circumferential stresses on the internal surface of the rotor do not exceed their intensity of 220 MPa, whereas compressive axial stresses in disc grooves (190 MPa) are maximum. During the cold start (CS) period and in gaining 100 MW of power, the stress intensity in the HPR amounts to 170 MPa on the internal surface and is maximal during the whole start-stop period.For a medium-pressure rotor (MPR), the maximum stresses take place during the cold start of the turbine unit and in gaining 250 MW of power. In this case, the maximum radial temperature drop of 140°C is observed in the region near the 1st stage. The isothermal lin...

АНОТАЦІЯ N. SHULZHENKO, P. GONTAROVSKIY, N. GARMASH. I. MELEZHYK EVALUATION OF THE CRACK DEVELOPMENT AT A CYCLIC LOADING OF PLATE ELEMENTS USING THE PARAMETERS OF SCATTERED DAMAGES OF THE MATERIAL ABSTRACT The purpose of these studies was to work out the methods for the computation of crack development in the plate and axisymmetric elements of structures at cyclic loading for the plasto-elastic arrangement using the conception of the accumulation of scattered damages in the material. The processes of sign-changing plasto-elastic deformation and crack resistance of the material were simulated at the crack tip using the smooth specimen fatigue test data. Thermal and stress-strain behaviors of the construction were determined in different loading modes using the method of final elements for several fixed crack depths. The material damage was estimated using the curves of low-cycle fatigue and those of the range of plastoelastic deformations on the would-be way of the crack development resorting to the hypothesis of linear summation. When the damageability reaches a critical value at the crack tip its depth is increased nonuniformly by a value of the specified step. This scientific paper gives consideration to the kinetics of the surface crack in the region exposed to the action of zerorepetition cyclic loading. The results were compared with the data obtained using the Paris equations. A satisfactory agreement of the data is observed. This technique can be used for the evaluation of the service life of the elements of steam turbines.Key words: crack kinetics, cyclic loading, the range of plasto-elastic deformations, low-cycle fatigue curves, and the method of final elements.

Рассматривается кинетика кольцевой трещины в цилиндре с разными уровнями циклического нагружения. Применяется предложенная ранее методика расчетной оценки развития трещин в пластинчатых и осесимметричных конструкциях при циклическом нагружении, которая основана на концепции накопления рассеянных повреждений в материале. Упруго-пластическое деформирование материала в районе трещины определяется с помощью метода конечных элементов, а повреждаемость оценивается с использованием диаграмм усталостного разрушения гладких цилиндрических образцов. Учитывается контакт берегов трещины при сжимающих нагрузках. Результаты согласуются с данными, полученными по методу Ньюмана. Предлагаемая методика может быть использована для оценки живучести элементов паровых турбин (тепловых канавок роторов на пуско-остановочных режимах, замковых соединений лопаток с дисками и др.).Ключевые слова: кинетика трещины, циклическая нагрузка, размахи упруго-пластических деформаций, кривые малоцикловой усталости, метод конечных элементов, коэффициент асимметрии цикла, контакт берегов трещины. П. П. ГОНТАРОВСЬКИЙ, М. Г. ШУЛЬЖЕНКО, Н. Г. ГАРМАШ, І. І. МЕЛЕЖИК МОДЕЛЮВАННЯ РОСТУ КІЛЬЦЕВОЇ ТРІЩИНИ В ЦИЛІНДРИЧНОМУ ЕЛЕМЕНТІ КОНСТРУКЦІЇ ПРИ ЦИКЛІЧНОМУ НАВАНТАЖЕННІРозглядається кінетика кільцевої тріщини в циліндрі при різних рівнях циклічного навантаження. Використовується запропонована раніше методика розрахункової оцінки розвитку тріщини в осесиметричних конструкціях при циклічному навантаженні, яка базується на концепції накопичення розсіяних пошкоджень у матеріалі. Пружно-пластичне деформування матеріалу в районі тріщини моделюється методом скінченних елементів, а руйнування оцінюється з використанням діаграм втомного руйнування гладких циліндричних зразків Враховується контакт берегів тріщини при стискаючих навантаженнях. Результати узгоджуються з даними, отриманими по методу Ньюмана. Запропонована методика може бути використана для оцінки живучості елементів парових турбін (теплових канавок роторів при пуско-зупинних режимах, замкових з'єднань лопаток з дисками та ін.).Ключові слова: кінетика тріщини, циклічне навантаження, розмахи пружно-пластичних деформацій, криві малоциклової втоми, метод скінченних елементів, коефіцієнт асиметрії циклу, контакт берегів тріщини. P.The purpose of these studies was to work out the methods for the computation of crack development in the plate and axisymmetric elements of structures at cyclic loading for the plasto-elastic arrangement using the conception of the accumulation of scattered damages in the material. In the domain in question, we simulated the processes of alternating-sign plasto-elastic deformation and the material crack resistance was estimated using the fatigue test data for smooth specimens. Thermal and elastically-deformed states of the structure were determined for different loading modes using the finite elements method. The material damageability was assessed for the curves of low-cycle fatigue and for the range of plasto-elastic deformations on the route of probable crack propagation using the hy...

The work is devoted to the development of methodologies for determining the thermal and thermal-stress states of the main equipment in dry container storage facilities for spent nuclear fuel. Storage facilities of this type are most common for spent fuel of nuclear power reactors. The safety of storage equipment in terms of assessing its service life is not covered widely enough in the world scientific literature. In particular, there are no effective methods for calculating the thermal and thermal-stress states of the equipment that would take into account the influence of many external factors throughout the life of a storage facility. To assess the thermal state of the containers, forward conjugate heat transfer problems, accounting for the mutual heat transfer in both a solid body and in the fluid environment (air), are proposed to be solved. Based on the solution of the conjugate heat transfer problems, the boundary conditions are to be determined to further assess the thermal-stress state of storage containers using inverse heat transfer problems. The proposed approach to determining the thermal and thermal-stress states of a concrete spent fuel container will promote more effective methods for assessing the service life of dry spent fuel storage facilities, which is, in turn, necessary in the development of ageing management programs for storage equipment and long-term safe operation.