The aim of the research is the development and verification of a micromechanically motivated mode... more The aim of the research is the development and verification of a micromechanically motivated model of elastoplastic deformation of two-phase single-crystal nickel-based alloys, predicting behavior under high-temperature thermomechanical actionswith taking into account the presence of γ and γ' phases. The model is relevant for computations of the stress-strain state of cooled single crystal blades of gas turbine units. The constitutive equations for each of the phases took into account the anisotropy of elastic and plastic properties, the presence of octahedral slip systems, features of the cubic system, and various hardening mechanisms, including kinematic, isotropic and latent ones. The identification of the elastic and plastic constants of the material for the γ and γ 'phases was carried out on the basis of the known stress-strain curves for each phase. The determination of the effective properties and deformation diagrams of a two-phase single-crystal alloy, taking into a...
На основе экспериментальных данных в работе промоделирован процесс искрового плазменного спекания... more На основе экспериментальных данных в работе промоделирован процесс искрового плазменного спекания (ИПС) металлических частиц методом конечных элементов в термоэлектромеханической постановке с учетом влияния температуры на параметры материалов (никеля и меди). Сравнение результатов моделирования с экспериментом позволило создать вычислительную модель процесса ИПС, удобную для оценки влияния параметров ползучести и пластичности на размер межчастичной шейки, образующейся при проведении ИПС. Установлено, что для высоких температур эффект ползучести в несколько раз превосходит влияние пластичности на процесс образования шейки спекания. При этом изменение параметров ползучести при моделировании также активно влияет на формирование шейки.
VESTNIK of Samara University. Aerospace and Mechanical Engineering, 2015
The peculiarities of short-term resistance to tension/compression, creep, long-term strength and ... more The peculiarities of short-term resistance to tension/compression, creep, long-term strength and thermal fatigue of single-crystal superalloys for different crystallographic orientations and temperatures are considered. The failure criteria are proposed using a unified measures equivalent stress (strain) for the cubic system, allowing to compute adequate strength and durability of single crystal materials under complex multi-axial inhomogeneous stress state, which is characteristic for gas turbine engine blades during the operation.
In order to improve the accuracy of the strength analysis of reinforced concrete structures, it i... more In order to improve the accuracy of the strength analysis of reinforced concrete structures, it is rational to use the model with a discrete location of reinforcing bars with the actual characteristics of adhesion to concrete reinforcement. The problem of pulling the reinforcing bar from the concrete block is actual for the practice, as it represents the most widespread method of experimental evaluation of characteristics of reinforced-concrete bond behavior. Fracture process of bonds at pulling the rebar from the concrete is a complex multistep process, accompanied by the presence of inhomogeneous and inelastic deformation, a rupture of adhesive bonds, the initiation and propagation of cracks of different shape and orientation, the presence of contact and tribological phenomena. The nonlinear finite-element solutions of the problem of pulling the reinforcing bar from the concrete block have been obtained with using various models of bond behavior and concrete cracking. The comparis...
The actual problem of the crack growth prediction in anisotropic elastic and inelastic materials ... more The actual problem of the crack growth prediction in anisotropic elastic and inelastic materials has not been fully investigated neither theoretically nor experimentally. In particular the analysis of crack growth in single-crystal gas-turbine blades is of great interest to assess their strength and durability. The present research is devoted to the comparison of various linear and nonlinear fracture mechanics criteria of the crack propagation in anisotropic materials under different loading conditions (fatigue, thermal fatigue and creep) with published experimental data. The computational features of the stress intensity factors (SIF) K I , K II , K III , resolved shear SIF K rss , J-integral and C * -integral for anisotropic materials in the framework of the finite-element analysis is considered. Verification of implemented procedures for fracture mechanics parameters is carried out on tension specimens of different crystallographic orientations. The results of the edge crack in t...
The influence of the domain structure’s initial topology and its evolution on the hysteresis curv... more The influence of the domain structure’s initial topology and its evolution on the hysteresis curves of tetragonal and rhombohedral polydomain structures of ferroelectroelastic materials is studied. Based on the analysis of electrical and mechanical compatibility conditions, all possible variants of representative volume elements of tetragonal and rhombohedral second-rank-domain laminate structures were obtained and used in simulations. Considerable local inhomogeneity of stress and electric fields within the representative volume, as well as domain interaction, necessitates the use of numerical methods. Hysteresis curves for laminated domain patterns of the second rank were obtained using finite-element homogenization. The vector-potential finite-element formulation as the most effective method was used for solving nonlinear coupled boundary value problems of ferroelectroelasticity. A significant anisotropy of the hysteresis properties of domain structures was established both withi...
Results of long-term hydrostatic strength study of piping systems made from polyethylene with inc... more Results of long-term hydrostatic strength study of piping systems made from polyethylene with increased temperature resistance PE-RT type II of Hostalen 4731B without reinforcement are presented and discussed in this paper. The different approximations of durability curves and various equivalent stress measures are considered and compared. An analytical expression for the maximum allowable internal pressure as function of service life of pipes, temperature, geometrical parameters of pipe cross-section and material properties is given. Pipes without reinforcement with nominal outer diameters from 32 mm to 225 mm were analyzed to assess long-term hydrostatic strength using equivalent stress, provided that there is no change in mechanism of damage accumulation. This allowed us to use linear extrapolation into area of long service life. The results indicate possible use of pipes SDR7.4 in heating networks for 50 years with heat transfer fluid parameters of 95 °C and internal pressure of...
Bone is a hierarchically structured material with mechanical properties depending on its morpholo... more Bone is a hierarchically structured material with mechanical properties depending on its morphological parameters at all levels of hierarchy. At a nanolevel, bone is a composite with a quasiperiodic structure, consisting of hydroxyapatite crystals, which are embedded into the collagen fibrils. The purpose of the paper is to analyze the influence of the nanostructure of bone on its elastic and strength properties. Such studies are important for the creating artificial bone-substitute materials. The new morphological nanoscale model of bone is proposed with taking into ac-count the mineral bridges between the associations of the hydroxyapatite crystals. The analysis of variation influence in the morphological characteristics (hydroxyap-atite crystals disorientation, sizes and orientation of mineral bridges, mineralization) on the local stress-strain state and mechanical properties of the representative vol-ume element of bone is carried out by means of the direct finite element simula...
The high-pressure turbine blades of most modern gas turbine engines are made of single-crystal al... more The high-pressure turbine blades of most modern gas turbine engines are made of single-crystal alloys. Single-crystal materials have significant anisotropy characteristics; therefore, the orientation of the axes of the single crystal relative to the geometrical axes of the blade has a great effect on the stress-strain state, static strength, and dynamic characteristics of the blade. Here, the necessary optimization of both the axial orientation (the optimal value of which may differ from <001>) and the azimuthal orientation is confirmed. The problem was solved by considering the anisotropic temperature–orientation characteristics of the alloy and the uneven temperature field of the blade. The values of the optimal crystallographic orientations were determined. Notably, casting tolerances for the deviation of the crystallographic axes must be considered when searching for the optimal position of the axes of the single crystal.
To determine the load-carrying capacity of the drillpipe slip, it is necessary to calculate the d... more To determine the load-carrying capacity of the drillpipe slip, it is necessary to calculate the drag force on the surface between the pipe and the slip. To improve such capacity, the grip surface is provided with teeth that can indent into the pipe body. As a result, the friction force on the contact surface is supplemented with the drag force generated by plastic shear strain of the pipe body. The paper presents an analytic dependence of the indentation force of an ideal (untruncated) and non-ideal (truncated) wedge punch that models tooth operation on the indentation depth and friction factor on the punch lateral face both for shallow (with prevailing elastic strain of the gripped body) and deep indentation (with prevailing plastic strain). Multiple computational experiments were performed to identify parameters of the proposed formula. Such computations were complemented with determination of the punch drag force dependence on the indentation depth during punch shearing. The deve...
На основе использования четырехчленного деформационного критерия термоусталостной прочности предл... more На основе использования четырехчленного деформационного критерия термоусталостной прочности предложен экстраполяционный метод прогнозирования долговечности жаропрочных монокристаллических сплавов при термоциклическом нагружении для диапазона температур, расширенного по сравнению с экспериментальным в область более низких температур. Проведена верификация предложенного подхода по результатам отдельных испытаний жаропрочных монокристаллических сплавов на никелевой основе ЖС32, ЖС36 и ВЖМ4-ВИ при различных максимальных и минимальных температурах цикла, при наличии и отсутствии выдержек для плоских корсетных образцов различных кристаллографических ориентаций. Показано, что ошибка в определении числа термических циклов до образования магистральных трещин не превышает один порядок, в то время как использование получившей широкое распространение на практике формулы универсального наклона Мэнсона может превышать два-три порядка.
The methodology for identification of mechanical characteristics of the nonlinear material model ... more The methodology for identification of mechanical characteristics of the nonlinear material model for concrete, taking into account the elastic-plastic deformation and the damage accumulation under monotonous and cyclic loading, is proposed. The using such improved models of concrete deformation is actual for carrying out finite-element computations of the most important elements of unique and responsible buildings and structures. The proposed methodology is verified for three different types of concrete (B45, B25, B5), including also their preliminary heat treatment at 200 °C, 300 °C, 400 °C and 600 °C. The experiments were carried out on standard specimens of cubic and prismatic form under compression, as well as on dog-bone-shaped specimens under tension. Elasticity and plasticity moduli, ultimate strengths in compression and tension, damage evolutions during deformation process were obtained in tests. Particular attention has been paid to the search for reliable and effective met...
The aim of the research is the development and verification of a micromechanically motivated mode... more The aim of the research is the development and verification of a micromechanically motivated model of elastoplastic deformation of two-phase single-crystal nickel-based alloys, predicting behavior under high-temperature thermomechanical actionswith taking into account the presence of γ and γ' phases. The model is relevant for computations of the stress-strain state of cooled single crystal blades of gas turbine units. The constitutive equations for each of the phases took into account the anisotropy of elastic and plastic properties, the presence of octahedral slip systems, features of the cubic system, and various hardening mechanisms, including kinematic, isotropic and latent ones. The identification of the elastic and plastic constants of the material for the γ and γ 'phases was carried out on the basis of the known stress-strain curves for each phase. The determination of the effective properties and deformation diagrams of a two-phase single-crystal alloy, taking into a...
На основе экспериментальных данных в работе промоделирован процесс искрового плазменного спекания... more На основе экспериментальных данных в работе промоделирован процесс искрового плазменного спекания (ИПС) металлических частиц методом конечных элементов в термоэлектромеханической постановке с учетом влияния температуры на параметры материалов (никеля и меди). Сравнение результатов моделирования с экспериментом позволило создать вычислительную модель процесса ИПС, удобную для оценки влияния параметров ползучести и пластичности на размер межчастичной шейки, образующейся при проведении ИПС. Установлено, что для высоких температур эффект ползучести в несколько раз превосходит влияние пластичности на процесс образования шейки спекания. При этом изменение параметров ползучести при моделировании также активно влияет на формирование шейки.
VESTNIK of Samara University. Aerospace and Mechanical Engineering, 2015
The peculiarities of short-term resistance to tension/compression, creep, long-term strength and ... more The peculiarities of short-term resistance to tension/compression, creep, long-term strength and thermal fatigue of single-crystal superalloys for different crystallographic orientations and temperatures are considered. The failure criteria are proposed using a unified measures equivalent stress (strain) for the cubic system, allowing to compute adequate strength and durability of single crystal materials under complex multi-axial inhomogeneous stress state, which is characteristic for gas turbine engine blades during the operation.
In order to improve the accuracy of the strength analysis of reinforced concrete structures, it i... more In order to improve the accuracy of the strength analysis of reinforced concrete structures, it is rational to use the model with a discrete location of reinforcing bars with the actual characteristics of adhesion to concrete reinforcement. The problem of pulling the reinforcing bar from the concrete block is actual for the practice, as it represents the most widespread method of experimental evaluation of characteristics of reinforced-concrete bond behavior. Fracture process of bonds at pulling the rebar from the concrete is a complex multistep process, accompanied by the presence of inhomogeneous and inelastic deformation, a rupture of adhesive bonds, the initiation and propagation of cracks of different shape and orientation, the presence of contact and tribological phenomena. The nonlinear finite-element solutions of the problem of pulling the reinforcing bar from the concrete block have been obtained with using various models of bond behavior and concrete cracking. The comparis...
The actual problem of the crack growth prediction in anisotropic elastic and inelastic materials ... more The actual problem of the crack growth prediction in anisotropic elastic and inelastic materials has not been fully investigated neither theoretically nor experimentally. In particular the analysis of crack growth in single-crystal gas-turbine blades is of great interest to assess their strength and durability. The present research is devoted to the comparison of various linear and nonlinear fracture mechanics criteria of the crack propagation in anisotropic materials under different loading conditions (fatigue, thermal fatigue and creep) with published experimental data. The computational features of the stress intensity factors (SIF) K I , K II , K III , resolved shear SIF K rss , J-integral and C * -integral for anisotropic materials in the framework of the finite-element analysis is considered. Verification of implemented procedures for fracture mechanics parameters is carried out on tension specimens of different crystallographic orientations. The results of the edge crack in t...
The influence of the domain structure’s initial topology and its evolution on the hysteresis curv... more The influence of the domain structure’s initial topology and its evolution on the hysteresis curves of tetragonal and rhombohedral polydomain structures of ferroelectroelastic materials is studied. Based on the analysis of electrical and mechanical compatibility conditions, all possible variants of representative volume elements of tetragonal and rhombohedral second-rank-domain laminate structures were obtained and used in simulations. Considerable local inhomogeneity of stress and electric fields within the representative volume, as well as domain interaction, necessitates the use of numerical methods. Hysteresis curves for laminated domain patterns of the second rank were obtained using finite-element homogenization. The vector-potential finite-element formulation as the most effective method was used for solving nonlinear coupled boundary value problems of ferroelectroelasticity. A significant anisotropy of the hysteresis properties of domain structures was established both withi...
Results of long-term hydrostatic strength study of piping systems made from polyethylene with inc... more Results of long-term hydrostatic strength study of piping systems made from polyethylene with increased temperature resistance PE-RT type II of Hostalen 4731B without reinforcement are presented and discussed in this paper. The different approximations of durability curves and various equivalent stress measures are considered and compared. An analytical expression for the maximum allowable internal pressure as function of service life of pipes, temperature, geometrical parameters of pipe cross-section and material properties is given. Pipes without reinforcement with nominal outer diameters from 32 mm to 225 mm were analyzed to assess long-term hydrostatic strength using equivalent stress, provided that there is no change in mechanism of damage accumulation. This allowed us to use linear extrapolation into area of long service life. The results indicate possible use of pipes SDR7.4 in heating networks for 50 years with heat transfer fluid parameters of 95 °C and internal pressure of...
Bone is a hierarchically structured material with mechanical properties depending on its morpholo... more Bone is a hierarchically structured material with mechanical properties depending on its morphological parameters at all levels of hierarchy. At a nanolevel, bone is a composite with a quasiperiodic structure, consisting of hydroxyapatite crystals, which are embedded into the collagen fibrils. The purpose of the paper is to analyze the influence of the nanostructure of bone on its elastic and strength properties. Such studies are important for the creating artificial bone-substitute materials. The new morphological nanoscale model of bone is proposed with taking into ac-count the mineral bridges between the associations of the hydroxyapatite crystals. The analysis of variation influence in the morphological characteristics (hydroxyap-atite crystals disorientation, sizes and orientation of mineral bridges, mineralization) on the local stress-strain state and mechanical properties of the representative vol-ume element of bone is carried out by means of the direct finite element simula...
The high-pressure turbine blades of most modern gas turbine engines are made of single-crystal al... more The high-pressure turbine blades of most modern gas turbine engines are made of single-crystal alloys. Single-crystal materials have significant anisotropy characteristics; therefore, the orientation of the axes of the single crystal relative to the geometrical axes of the blade has a great effect on the stress-strain state, static strength, and dynamic characteristics of the blade. Here, the necessary optimization of both the axial orientation (the optimal value of which may differ from <001>) and the azimuthal orientation is confirmed. The problem was solved by considering the anisotropic temperature–orientation characteristics of the alloy and the uneven temperature field of the blade. The values of the optimal crystallographic orientations were determined. Notably, casting tolerances for the deviation of the crystallographic axes must be considered when searching for the optimal position of the axes of the single crystal.
To determine the load-carrying capacity of the drillpipe slip, it is necessary to calculate the d... more To determine the load-carrying capacity of the drillpipe slip, it is necessary to calculate the drag force on the surface between the pipe and the slip. To improve such capacity, the grip surface is provided with teeth that can indent into the pipe body. As a result, the friction force on the contact surface is supplemented with the drag force generated by plastic shear strain of the pipe body. The paper presents an analytic dependence of the indentation force of an ideal (untruncated) and non-ideal (truncated) wedge punch that models tooth operation on the indentation depth and friction factor on the punch lateral face both for shallow (with prevailing elastic strain of the gripped body) and deep indentation (with prevailing plastic strain). Multiple computational experiments were performed to identify parameters of the proposed formula. Such computations were complemented with determination of the punch drag force dependence on the indentation depth during punch shearing. The deve...
На основе использования четырехчленного деформационного критерия термоусталостной прочности предл... more На основе использования четырехчленного деформационного критерия термоусталостной прочности предложен экстраполяционный метод прогнозирования долговечности жаропрочных монокристаллических сплавов при термоциклическом нагружении для диапазона температур, расширенного по сравнению с экспериментальным в область более низких температур. Проведена верификация предложенного подхода по результатам отдельных испытаний жаропрочных монокристаллических сплавов на никелевой основе ЖС32, ЖС36 и ВЖМ4-ВИ при различных максимальных и минимальных температурах цикла, при наличии и отсутствии выдержек для плоских корсетных образцов различных кристаллографических ориентаций. Показано, что ошибка в определении числа термических циклов до образования магистральных трещин не превышает один порядок, в то время как использование получившей широкое распространение на практике формулы универсального наклона Мэнсона может превышать два-три порядка.
The methodology for identification of mechanical characteristics of the nonlinear material model ... more The methodology for identification of mechanical characteristics of the nonlinear material model for concrete, taking into account the elastic-plastic deformation and the damage accumulation under monotonous and cyclic loading, is proposed. The using such improved models of concrete deformation is actual for carrying out finite-element computations of the most important elements of unique and responsible buildings and structures. The proposed methodology is verified for three different types of concrete (B45, B25, B5), including also their preliminary heat treatment at 200 °C, 300 °C, 400 °C and 600 °C. The experiments were carried out on standard specimens of cubic and prismatic form under compression, as well as on dog-bone-shaped specimens under tension. Elasticity and plasticity moduli, ultimate strengths in compression and tension, damage evolutions during deformation process were obtained in tests. Particular attention has been paid to the search for reliable and effective met...
Uploads
Papers