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The addition of fibers helps to increase the performance of concrete in terms of resistance and flexibility. Different types of fibers that have different mechanical properties may change the behavior of concrete. Fiber-reinforced concrete with varied combinations of fibers (steel, macro synthetic, and polypropylene fibers) in 1% volume is investigated in this research. Concrete samples were fabricated from a combination of two types of fibers with different percentages to measure the compressive strength with the approach of determining the optimal ratio of fibers. The results showed that the hybrid samples containing steel fibers provide higher compressive strength compared to the samples containing macro synthetic and polypropylene fibers. Macro synthetic and polypropylene fibers in concrete samples have played a significant role in increasing the flexibility and efficiency of concrete, as well as significantly reducing cracking and increasing durability and toughness. In these hybrid models, coherence is preserved in the event of failure. The combination of polypropylene fibers with both steel and macro synthetic fibers significantly reduces the compressive strength of concrete samples. In concrete samples with hybrid fibers, samples with a combination of macro synthetic and steel fibers had higher compressive strength than samples with a combination of steel and polypropylene fibers. [ABSTRACT FROM AUTHOR]

The nickel content effects on the strength, plasticity, and low-cycle life of hardened and aged specimens of different modifications of austenitic iron-nickel steels and alloys in the initial state and after preliminary high-temperature hydrogenation in hydrogen at a pressure of 30 MPa and temperatures of 293, 773 and 973 K were studied. At 293 K, hydrogen embrittlement of hardened materials weakens with increasing nickel concentration from 10 to 23 wt.%; it is insignificant in the concentration range of 23–45 wt.% and significantly increases with higher nickel content. After aging, materials with a nickel content of 23 and 36 wt.% are insensitive to the action of the hydrogen environment; at higher hydrogen concentrations, embrittlement intensifies. The structural state of aged materials significantly affects the degree of hydrogen embrittlement of their various modifications during short-term tensile tests and slightly less during low-cycle fatigue tests. In the range of Ni concentrations of 23–73 wt.%, the effect of hydrogen on the relative transverse narrowing remains almost stable. The relative elongation of more hydrogen-resistant modifications of materials and low-cycle life increases with increasing nickel content. At 773 K, the effect of nickel content on the relative transverse narrowing in gaseous hydrogen at a pressure of 30 MPa is slightly smaller but qualitatively the same as at 293 K. At 973 K, more heat-resistant high-nickel alloys embrittle in a hydrogen environment much more strongly than hard dispersion steels. Thermomechanical treatment, according to the quenching scheme, tension at room temperature, and aging for 16 h at 973 K significantly increases the plasticity of materials in the presence of hydrogen at the same strength. [ABSTRACT FROM AUTHOR]

The validity conditions of nonlinear problems of mechanics of elastic-plastic deformation, which take into account the evolution of the growth of the volume of nucleated pores in the material based on the generalized Rice–Tracey–Huang equation, are investigated. This equation combines the classical Rice–Tracey–Huang equations, in which an additional continuous function greater than zero is introduced, which depends on the stiffness of the stress state and has a nonnegative derivative. With this modification of the classical Huang equation, the properties of the governing equations for the analysis of the porosity of irradiated material are improved, which contributes to the weakening of the restrictions on the initial data associated with the stiffness of the stress state. Using the generalized Rice–Tracey–Huang equation, the governing equations of material behavior are formulated to describe the nonisothermal processes of elastic-plastic deformation, taking into account the increase in the concentration of ductile fracture pores in the material. The loading process is divided into separate calculation stages, and for each of them, the plastic flow equation and the generalized Rice–Tracey–Huang equation are integrated for the loading stage. Due to integration, the governing equations for the full stress and strain components are obtained, which allows us to describe the processes of active loading, unloading, and reloading. Irreversible deformations in these equations include accumulated plastic deformations and structural volumetric deformations that take into account the concentration of pores in the material. The conditions are formulated under which the dissipation power and the power developed by the additional stresses on the additional deformations caused by them do not decrease in the process of loading the porous material. On the basis of the obtained energy inequalities, which generalize the postulate of Drucker's strengthening in relation to the porous material, the conditions are established that ensure the correctness of the formulated plasticity equations, which take into account the growth of pore concentration in the material on the basis of the generalized Rice–Tracey–Huang equation. [ABSTRACT FROM AUTHOR]

Validity conditions in nonlinear problems of elastic-plastic deformation mechanics, taking into account the process of nucleated pore volume growth in the material via Huang's equation, are investigated. The constitutive equations of material behavior are formulated, making it possible to describe nonisothermal processes of elastic-plastic deformation, considering the growth of viscous fracture pore concentration. The loading process is subdivided into separate computational steps; for each, the plastic flow equation and Huang's equation are integrated over the loading step. The constitutive equations for the total stress and strain components are derived through integration to describe the processes of active loading, unloading, and reloading. The irreversible strains in these equations include accumulated plastic strains and structural bulk strains, which account for the concentration of pores in the material via Huang's equation. The performed analysis of the properties of the constitutive equations made it possible to formulate conditions under which the dissipation power and the power developed by the additional stresses on the additional deformations caused by them do not decrease during the porous material loading. Based on the obtained energy inequalities generalizing Drucker's postulate of hardening for porous materials, this study established the conditions ensuring the validity of the formulated equations of plasticity, which take into account the pore volume growth via Huang's equation. [ABSTRACT FROM AUTHOR]

The conditions that ensure the validity of nonlinear problems of elastic-plastic deformation mechanics, taking into account the growth of nucleated pore volume in the material via the Reiss–Tracey model, are investigated. Using this model, the determinants of material behavior are formulated, making it possible to describe nonisothermal processes of elastic-plastic deformation considering the increased concentration of viscous fracture pores. The loading process is broken down into separate computational stages, within which the plastic flow equation and pore concentration growth equations via the specified model are integrated over the loading stage. Through integration, the constitutive equations for the full stress and strain components are derived, allowing one to describe the active loading, unloading, and re-loading processes. The irreversible strains in these equations include accumulated plastic strains and structural bulk strains, which account for the pore concentration in the material via the Reiss–Tracey model. The solution of practical problems via the formulated equations promotes the persistence of computational processes, making it possible to use extended loading stages in calculations. At the same time, the analysis of properties of the obtained determinative equations is simplified in comparison with the equations of plasticity in finite increments. Conditions are formulated, in which the dissipation power and the power developed by additional stresses and stress-induced on additional strains do not drop during the loading of porous materials. On the basis of the obtained energy inequalities, which generalize Drucker's postulate with respect to the porous material, conditions are established that ensure the correctness of the formulated plasticity equations, which take into account the pore volume growth via the Reiss–Tracey model. [ABSTRACT FROM AUTHOR]

The geometrical form of the solid indenter is a very important factor to determine some physical and mechanical proprieties such as hardness, elastic modulus, contact surface area, as well as tribological parameters of the tested materials. This study compared the volume and the surface of the imprint that resulted from a novel tip penetrator (prolate spheroid chap) with the spherical chaps. Firstly, general mathematical concepts of ellipsoid, spheroid, and spherical indentors are discussed, and the respective expressions of the volume of a body of revolution are derived. Secondly, expressions and geometric forms of imprint surfaces and volumes resulting from prolate spheroid and spherical indenters are determined as functions of their depth or diameter. Finally, a comparative study on application of prolate spheroid and spherical indenters of the same depth is conducted showing the advantages of the former over the latter. [ABSTRACT FROM AUTHOR]

The paper presents the results of an analysis of the correctness of constitutive equations of irradiation creep, which describe non-isothermal processes of inelastic deformation, taking into account the irradiation swelling and irradiation creep of material under the conditions of neutron irradiation, high temperatures, and damaging dose. Current models of irradiation swelling and irradiation creep, which take into account the damaging dose, irradiation temperature, and the effect of stress state and accumulated irreversible strain on the processes of swelling and creep of material, are considered. The conditions under which dissipation power and the power developed by additional stresses on additional deformations do not decrease during loading under neutron irradiation conditions have been studied. On the basis of the obtained energy inequalities, which generalize Drucker's postulate for the irradiated material, the conditions that ensure the correctness of the formulated creep equations have been determined. The results of an analysis of the correctness conditions for irradiation creep equations showed that taking into account accumulated irreversible strain in the confined swelling model contributes to the relaxation of restrictions on the possible swelling of the material and initial data, which ensure the correctness of the constitutive equations of irradiation creep. [ABSTRACT FROM AUTHOR]

The experimental uniaxial cyclic loading diagram for a 40Kh16N9G2S steel specimen was analyzed to define the three sections representing different stress behavior, i.e., three different stress modes. For each stress mode, the corresponding evolutionary equations governing anisotropic hardening were formulated. For describing the isotropic hardening, the evolutionary equation for the second-mode saturation parameter is introduced. The stress deviator is defined as the sum of stress deviators of the three modes. The nonlinear damage accumulation is represented by the kinetic equation based on the energy principle, where the energy equal to the work of second-mode stresses within the strain field is taken as the energy spent for damaging of the material. The material functions governing the theory are defined, the basic experiment and the identification method of the material functions are formulated. The material functions of 40Kh16N9G2S steel and theory verification results under proportional strain-controlled cyclic loading and nonproportional loading along the strain path in the form of concentric circles with the common center in the origin of coordinates are presented. Five path turns are examined, starting from the large-curvature path to the mean-curvature one. Computational and experimental results are in close agreement. [ABSTRACT FROM AUTHOR]

The results of an analysis of the correctness of constitutive equations of irradiation creep which describe non-isothermal processes of inelastic deformation taking into account radiation swelling and radiation creep of material under the conditions of neutron irradiation, high temperatures and damaging dose, are presented. Modern models of radiation swelling and radiation creep, which take into account the damaging dose, irradiation temperature, and the influence of stress state on the processes of swelling and creep of irradiated material are considered. Using these models, constructive equations are formulated, which allow the processes of inelastic deformation to be described taking into account the radiation swelling and radiation creep strains of the material. The conditions under which the equations of radiation creep are consistent with the principle of irreversibility of inelastic deformation power increment are investigated. Based on the results of the analysis of the properties of constitutive equations, the necessary and sufficient conditions under which the power of dissipation and the power which is developed by additional stresses on additional deformations do not decrease during the loading of the irradiated material have been determined. On the basis of the obtained energy inequalities, which generalize Drucker's postulate concerning the irradiated material, and the general results of the analysis of the properties of nonlinear operators, the conditions that ensure the correctness of the formulated creep equations have been determined. It was found that taking into account radiation creep strains contributes to the relaxation of restrictions on the initial data, which ensure the correctness of the constiyive equations. According to the a priori estimates obtained, the duration of loading stages is determined not only by the data on the convergence and accuracy of the solution of creep equations, which describe the process of deformation of irradiated material, but also by the conditions under which they can be solved. We present a priori estimates of the maximum permissible value of the damaging dose for austenitic 08Kh18N10T steel at different irradiation temperatures. In strength calculations, such estimates are useful at the stage of problem statement to analyze the adequacy of initial data. [ABSTRACT FROM AUTHOR]

Modern models of irradiation swelling and irradiation creep are considered, in which the damaging dose, irradiation temperature, and influence of stress state on swelling and creep of irradiated material are taken into account. Using these models, constitutive equations of material behavior are formulated, which makes it possible to describe the non-isothermal processes of inelastic strain, taking into account irradiation swelling and irradiation creep strains. The loading process is broken down into separate computational stages, and for each of them the equations of plastic flow and irradiation creep are integrated within the loading stage. Through integration, constitutive equations for the full stress and strain components are derived, which allows the processes of active loading, unloading, and reloading to be described. The irreversible strains in these equations include accumulated plastic strains, irradiation swelling, and irradiation creep strains. The derived equations are treated as constitutive equations for irradiation creep, in which creep strain is defined as strain that includes instantaneous plastic strain and creep strain. Elastic-plastic strain curves that take into account the accumulated damaging dose and irradiation temperature are transformed into a functional dependence that describes the strain of irradiated material depending on the intensity of irradiation creep strain growth during the loading stage. The application of the formulated equations to the solution of practical problems contributes to the persistence of computational processes that makes it possible to use extended loading stages for calculations. At the same time, the study of the properties of the obtained constitutive equations is considerably simplified in comparison with the analysis of plasticity and creep equations in finite increments. Initial prerequisites for the formulation of constitutive equations of irradiation creep based on the full model of swelling, which takes into account the accumulated irreversible strain, are outlined. [ABSTRACT FROM AUTHOR]

The results of an experimental study of the mechanical properties of carbon fiber-reinforced plastics (CFRP) made by the "wet" winding method in the temperature range of room temperature to −196°C with different reinforcement schemes are presented. The temperature dependences of strength, plasticity and elasticity characteristics of these materials in tensile and three-point bending tests are obtained. The elastic modulus of CFRP with a longitudinal scheme of reinforcement in a given temperature range is at the level of 160 GPa. The ultimate stress of the material at room temperature is 1370 MPa. The temperature dependence of this characteristic is close to linear and practically coincides with that of bending. The low-temperature hardening, estimated by the change in the value of the ultimate stress due to cooling, reaches 39%. The mechanical characteristics of CFRP with a transverse reinforcement scheme both in tension and in bending in the considered temperature range have rather low values and are determined mainly by the matrix properties. When cooling from 20 to −196°C, the elastic modulus of CFRP with a ±45° reinforcement scheme increases by 55%, and its low-temperature hardening is 40%. At the same time, the elastic modulus and ultimate stress are six to eight and ten times, respectively, lower than the similar characteristics of CFRP with the longitudinal reinforcement scheme. Fracture of such a composite at all investigated temperatures occurs locally by shifting at an angle of 45° because of delamination of the material. [ABSTRACT FROM AUTHOR]

Mathematical simulation of elastoplastic deformation of additionally isotropically hardened materials under proportional and nonproportional cyclic loadings is examined. A rather simple version of the plasticity theory, being a special case of the theory of inelasticity, is discussed. This version belongs to the class of single-surface combined-hardening flow theories. The results of computational and experimental investigations of elastoplastic deformation and fatigue fracture of materials at various nonproportional cyclic loads are cited. An adequate description of nonproportional loading processes, additional isotropic hardening effects, as well as fracture processes within one, rather simple version of the plasticity theory is by for the advantage of examined mathematical simulation. [ABSTRACT FROM AUTHOR]

The strength properties of cast solid-solution high-entropy alloys based on bcc and fcc lattices in the temperature range from -70 to 900°C have been investigated. Melting ingots weighing up to 200 g were carried out in a vacuum-arc furnace MIFI-9 by melting the mixture in an atmosphere of purified argon with a non-consumable tungsten electrode on a water-cooled copper hearth. The X-ray phase analysis and scanning electron microscopy in combination with INCA X-ray microanalyzer were used. Hardness (HIT) and reduced elastic modulus (Er) were determined using automatic microindentation on a Micron-gamma device using the Berkovich pyramid with a 2 N load in accordance with ISO14577-1:2015. High-temperature indentation of the Vickers pyramid was carried out at a 9.8 N load in vacuum. Thehigh-entropy composition of Nb1.5Cr1.25MoV0.75Ta0.5, which is a solid solution based on the bcc lattice, is characterized by high values of hardness up to 900°C. The yield stress and plasticity of solid-solution alloys are determined depending on the temperatures of the compression tests and the type of crystal lattice. For the high-entropy composition TiZrHfVNbTa based on the bcc lattice, the yield points are almost twice as high as those of the CrMnFeCoNi composition based on the fcc lattice. To create high-entropy alloys with improved characteristics of hot hardness, it is necessary to take into account such factors as the melting point, enthalpy of mixing, and dimensional mismatch in the lattice. It was found that alloys based on bcc lattice at positive values of the enthalpy of mixing are characterized by high characteristics of plasticity and deformability, as well as normalized hardness HIT/Er and compressive yield strength at room temperature. This can be attributed to the cluster structure and distortion of the crystal lattice. [ABSTRACT FROM AUTHOR]

The authors present the results of experimental investigations of strength and plasticity characteristics, as well as fracture nature, of the specimens of different steels under tension after ion nitriding in hydrogen (nitrogen with hydrogen) and hydrogen-free (nitrogen with argon) environments. The obtained characteristics are compared with those before nitriding. It is established that during ion nitriding in the hydrogen-free environment, tensile strength of the specimens has increased by 4–11%, whereas relative elongation and contraction have decreased by 1.1–3 times based on the nitriding mode and steel type. The authors have built the tensile stress-strain diagram for the specimens made of steel St3, 40Kh, and 12Kh18N10T without chemical and thermal treatment, ion nitriding in the hydrogen and hydrogen-free environments. The influence of hydrogen concentration in the saturation environment on the strength and plasticity characteristics has been defined. Under concentrations higher than 10 vol.% there is embrittlement with the decrease of strength characteristics (to 15%) and a significant decrease of plasticity (to 40%) for low-alloyed steels. For high-alloyed steels, the negative influence of hydrogen on the strength characteristics does not increase by 3%, while the influence on the plasticity characteristics – by 8%. The authors have investigated the initiation and propagation of microcracks under external loading on the steel with nitride layers. [ABSTRACT FROM AUTHOR]

We present the investigation of permanent strain of steel specimen occurred when metallurgical transformations take place even under small stress applied externally lower than the yield stress of material. Three alloyed steel grades were investigated: THG2000 (Uddeholm, Sweden), 40Kh13 and 95Kh18 (GOST, Russia). All steel grades differ in carbon content and amount of alloying elements and behave differently when transformation occurs. This intensively increased plasticity of steel specimen was observed during bending test when bending stress was just 100 MPa and was less than 10% of yield strength of the steel. The steel specimens were heated to 900-1050°C temperature and then bent during air quenching. Plastic deflections were observed though all cooling process that involved martensitic transformation as well. Different effect of compression and tensile stresses on microstructure evolution during martensitic transformation was determined by X-ray analysis as both types of stresses were formed in bent specimens. [ABSTRACT FROM AUTHOR]

An increased fracture initiation barrier of brittle materials is examined by the example of test results for flat glass. The fracture resistance of this glass on the rectangular specimen edge chipping with conical diamond indenters of different tip radii (11-800 μm) was evaluated. Optical glasses (quartz and light crown) were used for comparison. A significant change in glass behavior on the edge chipping of their specimens is observed only with the indenter of an 11-μm tip radius. In this case, the crack resistance of glasses is equal to that measured in Vickers experiments. Any basic differences in the fracture behavior of glasses with the indenters of tip radii of 100 and more micrometers were not revealed. The prescratching of the glass specimen surface near its edge before its chipping was noticed to exert negative effect on crack resistance estimates since its characteristic fracture initiation barrier is damaged. [ABSTRACT FROM AUTHOR]

The article presents the investigation of plasticity and microstructure of hot work tool steel during martensitic transformation. Specimens were austenized, then air quenched. During cooling process the specimens were bent under 100 MPa stresses. There were three types of loading during cooling: continuous bending straight after withdrawing of sample from furnace (deformation of initial austenite, and then martensite formation under stresses); bending when martensitic transformation started (deformation of martensite); unloading when martensitic transformation started (main deformation of austenite - measurement of self-deformation). Plastic deflection of bending samples was measured during cooling until room temperature. The incoming martensitic transformation of the material showed significant increasing of plasticity. As bending caused two types of stresses - tensile and compression, its different influence on martensitic transformation was detected by specimen self-deformation. The microstructure of the stretched and compressed surfaces of the samples was determined by XRD, SEM, and EDS methods. [ABSTRACT FROM AUTHOR]

The results of investigations of the mechanical characteristics of molybdenum and niobium alloys and their welded joints, which are used in space-rocket hardware, have been generalized. The investigations were carried out under short-time, sustained static and low-cycle loading conditions on small time bases in a temperature range of 290-2270 K. [ABSTRACT FROM AUTHOR]

The results of investigations of the mechanical characteristics of tungsten, alloys and composite materials based on it, which are used in space-rocket hardware, have been generalized. The investigations were carried out under short-time, sustained static and low-cycle loading conditions on small time bases in a temperature range of 290-3020 K. [ABSTRACT FROM AUTHOR]

For a copper-tungsten microlayered composite material for electrical contact applications, which is prepared by electron-beam evaporation-condensation, the changes in its structure, conductivity, hardness, and mechanical properties in tension at room temperature and elevated temperatures are studied versus the tungsten content and heat treatment conditions. New morphological features of the condensed composite and the related changes in the material properties have been revealed. The conditions for the formation of structural defects and their influence on mechanical properties and fracture behavior of the material in tensile tests have been investigated. A relationship has been established between the tungsten content of the composite, its structure, strength, and hardness. [ABSTRACT FROM AUTHOR]

We discuss the effect of diffusion heat-resistant and condensation gradient thermal barrier coatings used for protection of gas turbine disk operating blades on mechanical characteristics (long- and short-term durability and plasticity at temperature of 1000°C) of specimens from ZhS32-VI heat-resistant alloy. We study the effect of isothermal annealing in air at temperature 1100°C during 240 h on mechanical characteristics of uncoated and coated specimens. We note the expediency of application of gradient thermal barrier coating consisting from external heat-insulating ceramic layer and thermostable heat-resistant metal layer, which provide temperature reduction of metal walls of cooled blades made from ZhS32-VI heat-resistant alloy with the purpose of achieving the required residual life. [ABSTRACT FROM AUTHOR]

Based on the Wilkins two-dimensional algorithm, a method is developed for the numerical study of the geometrically and physically nonlinear axially symmetrical dynamic stress-strain state of multilayer thick-walled cylindrical elastoplastic shells with different spiral reinforcement structures. A numerical study of the specific features in the nonlinear dynamic behavior of single-and two-layer cylinders is carried out for different reinforcement configurations and loading amplitudes. [ABSTRACT FROM AUTHOR]

The paper addresses the action of a high-temperature hydrogen-containing fluid on mechanical properties of a low-alloy carbon hypopearlitic steel 09G2S which is used for the manufacture of a gasoline-producing reactor vessel for a catalytic reformer unit. The vessel metal had 180,000 running hours at a hydrogen-containing fluid temperature 280°C and pressure 4.0 MPa. It is demonstrated that a long-term operation of the material in contact with gaseous hydrogen has caused its natural ageing. Further hydrogen saturation of test specimens at 580°C and 10 MPa for 17 h has resulted in a so-called hydrogen-induced strain hardening of the material. The influence of gaseous hydrogen on the state of carbide phases in the base metal and weld is studied by the x-ray spectrum analysis and nuclear gamma resonance method. The amount of a carbide phase (cementite) in steel has been found to grow due to natural ageing at elevated temperatures. The high-temperature hydrogen saturation makes the cementite decomposition process more intensive, and no cementite recovery occurs even when the material is heated up to 580°C. [ABSTRACT FROM AUTHOR]

We consider the thermomechanical bending of a circular plate with a lightweight filler that rests on an elastic foundation. To describe the kinematics of a plate pack which is asymmetrical in thickness, the broken normal hypotheses are accepted. The foundation reaction is described by the Winkler model. The load is local and symmetrical. A set of equilibrium equations is derived and its exact solution in terms of displacements is obtained. Numerical results for a three-layer metal-polymeric plate are presented. [ABSTRACT FROM AUTHOR]

The short-term static strength and momentary creep characteristics of low-alloyed molybdenum alloy VM-1 are investigated in the temperature range from 1820 to 2270 K. The creep strength values for the alloy were obtained for residual strain tolerances of 0.5 and 1.0%, the test durations of 102, 103, and 104 s at temperatures of 1820, 2120 and 2270 K. The empirical functional dependence is proposed to describe the correlation relation between the characteristics of short-term static strength, plasticity and momentary creep of the material in the thermomechanical range under study. [ABSTRACT FROM AUTHOR]

We present some results of prediction of creep rupture strength and plasticity for austenitic materials prior to and after irradiation with variable neutron flux rates, based on physicomechanical model as outlined in Part 1. The calculated results are compared with the available experimental data. [ABSTRACT FROM AUTHOR]

The structure, hardness, strength, and plasticity of a laminated composite nanomaterial of the copper-zirconium-yttrium-molybdenum system obtained by electron-beam evaporation and layered vapor condensation over a temperature range of 290–1070 K are studied. Correlation between the hardness and strength of the composite was established. [ABSTRACT FROM AUTHOR]

We describe the methods and results of investigation of the characteristics of strength and plasticity of a pilot batch of tubes made of KTTs-110 zirconium alloy under the conditions of short- and long-term static loading. The obtained results are compared with the same characteristics of É-110 alloy extensively used in the active zones of WWÉR-1000-type nuclear reactors. [ABSTRACT FROM AUTHOR]