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The alternate load path method for progressive collapse analysis ignores the cause and mechanism of member failure and its influence on the dynamic effect of the remaining structures. It must assume the location of member failure, which is unsuitable for grid structures with many members. In this paper, by using the double broken line follow-up strengthening model and the proposed VUMAT material constitutive model, taking the member instability and material failure as the member failure criteria and considering the geometric nonlinearity and material nonlinearity, the instantaneous member removal method for deleting the failure member in real time was proposed. On this basis, nonlinear dynamic analysis for a three-layer space truss was used to compare the effects of different member failure criteria on the structural responses, such as the member failure sequence and the occurrence time of the continuous structural collapse. The results show that when considering the instability of members, the initial member failure and the final progressive collapse occur earlier than when using the material failure criterion, which is more similar to the actual situation. Furthermore, the proposed VUMAT material constitutive model can apply to study the progressive collapse behavior of space truss structures. [ABSTRACT FROM AUTHOR]

Establishing a quantitative prediction model for the SCC crack growth rate of dissimilar metal welded joints at the safe end is very important for the safety evaluation of nuclear power structures. However, the SCC growth process is closely related to crack tip creep. In this paper, uniaxial tensile creep experiments under different stress are carried out on nickel base alloy 600, and the constitutive creep equation of nickel base alloy 600 is established. At the same time, the SCC crack tip creep field is analyzed using finite element software, and the effects of crack tip creep variables, creep rates, and material creep properties on the crack tip field are analyzed. Results show that nickel base alloy 600 occurs creep under high stress, and the creep rate in the crack tip region decreases with the crack inclination angle and the distance from the crack tip. The peak values of creep and creep rate appear directly in front of the crack propagation direction. Research results lay a foundation for establishing a quantitative prediction model of SCC. [ABSTRACT FROM AUTHOR]

The mechanical properties of the crack tip are vital for material safety evaluation. The weld material of welded joints is prone to work hardening during processing and installation, which changes the material mechanical properties and seriously affects the safety assessment of nuclear power welded joints. At the same time, nuclear power pipelines will creep under high temperatures and cause changes in the mechanical field at the crack tip. This paper obtains the mechanical properties of nickel-based alloy 182 in a nuclear power water environment. With the help of ABAQUS software, the change rules of the crack tip stress field and creep field under different hardening degrees are analyzed, and then the influence on crack tip creep and crack propagation rate is analyzed. Results show that increasing pre-hardening will increase the Mises stress around the crack tip, and the creep around the crack tip is expressed under pre-deformation, indicating that pre-hardening can accelerate the cracking of stress corrosion to a certain extent. Research has shown that the work hardening induced by the pre-deformation has an important influence on the creep rate at the crack tip, and the high creep zone is mainly concentrated in the direction of crack propagation. Under a certain work hardening rate, the crack growth will be accumulated. [ABSTRACT FROM AUTHOR]

One of the most important challenges of storing fluids in thin walled pressure vessels under internal pressure is preventing crack propagation. At low temperatures, steel shows brittle crack propagation characteristic, which is highly dangerous. In this paper, a new numerical model is presented, in order to investigate the reinforcement of a cracked thin walled pressure vessel by composite patch. The extended finite element method (XFEM) technique is used to model brittle crack propagation through the thickness of a thin-walled pressure vessel utilizing the multi-scaling technique. Crack propagation in the thickness of a pressure vessel was studied utilizing the combination of XFEM approach in fracture mechanics and multi-scaling technique. Then, the critical energy, which is the maximum strain energy that the pressure vessel can absorb before the brittle crack starts to propagate, was calculated using the numerical techniques of XFEM. In order to increase the critical energy, cohesive elements and composite patches with different stacking sequence, which were extracted from previous experimental and analytical studies, were used, and the best stacking sequence was identified using the current XFEM code. Moreover, the optimization was carried out using the traditional optimization technique for reinforcing with composite patches, which was based on the optimum ratio of the increased critical energy to the thickness of the reinforcement. Results obtained show that, keeping constant the reinforcing thickness and changing the stacking angle, the maximum energy capacity is increased by 7-11%. Also, by increasing the thickness of the reinforcement, a significant growth in strain energy capacity (up to 40%) is observed. The Hashin damage criterion was used to ensure that none of the laminas' damage during the crack propagation is critical. [ABSTRACT FROM AUTHOR]

Correction to: Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Rice-Tracey-Huang models. Chirkov should read: "Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Rice-Tracey-Huang models. In Strength of Materials, 54, No. 5, 767-775 (2022), the title of the paper "Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Reiss-Tracey-Huang models. [Extracted from the article]

The paper presents the results of the application of the refined calculation guidelines to the analysis of the stress-strain state and fracture resistance of the equipment elements of the NPP primary circuit system with WWER reactor, in particular, the cylindrical part and the zone of the reactor pressure vessel inlet nozzle, coolant collector welded joint in a steam generator, baffle, and reactor internals' shaft under the operating and emergency modes of thermomechanical loading. The calculation methodology is based on the use of the modern models and methods of solution to the nonlinear boundary tasks of non-isothermal thermal viscoplasticity and tasks of fracture mechanics using the refined mixed schemes of the finite element method with increased accuracy. They allow one to obtain reliable solutions to the tasks considering the deformation history of thermomechanical loading, modern concepts of fracture mechanics and approaches to the modeling of brittle-viscous fracture defects, irradiation swelling and creep of metal, as well as as the structural elements, under the conditions of elevated temperature, intensive neutron irradiation and nonstationary modes of thermomechanical loading. The authors obtained and analyzed the calculation results for the cylindrical part and zone of the inlet nozzle of the WWER-1000 reactor pressure vessel, coolant collector welded joint in a steam generator, baffle, and reactor internals' shaft using the proposed guidelines. The results imply the possibilities of the proposed recommendations and make it possible to analyze some general tendencies and features of the application of the refined calculation models to justify the strength and life extension of the NPP structural elements under investigation. [ABSTRACT FROM AUTHOR]

Correction to: Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Rice-Tracey-Huang models. The Reiss-Tracey model" by O.Y. Chirkov should read: "Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Rice-Tracey-Huang models. The online version of the original article can be found at https://doi.org/10.1007/s11223-022-00410-6 In Strength of Materials, 54, No. 3, 345-357 (2022), the title of the paper "Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Reiss-Tracey-Huang models. [Extracted from the article]

The main principle used by the designers of riveting joints is a shear condition of rivet material. In case of shear test of conventional riveting joints, their strength is determined by the mechanical properties of the fastener material. Hence, it is expedient to have more insight on the fracture mechanism of various joints during tensile tests. This paper discusses the strength of riveting joints of various sheet materials: DC01 steel, AW-5754 aluminum alloy, and their hybrid arrangements. We also analyze of the fracture mechanism of riveting joints in unilateral tensile tests of T-shaped specimens made of various sheet materials. The experimental results on the joint critical static load are compared with those obtained in the lap joint shear tests for the same rivet types. [ABSTRACT FROM AUTHOR]

This paper presents the results of the finite element study on the effect of length of the external bar at soffit on the flexural behavior of retrofitted RC beams. A reference beam specimen and five retrofitted beam specimens with external bar length as variable were analysed using ANSYS 12.0 software and the results are presented. Initial cracking, performance at yielding of internal bar and at ultimate stage, ductility behavior, formation and propagation of cracks were studied and reported in this paper. [ABSTRACT FROM AUTHOR]

The paper presents the experimental results of investigations using different types of glass by the Rockwell indenter scratching of the specimen surface till its edge chipping (S+EF method). The peculiar features of the materials' fracture are determined as a result of fractography analysis of the empirical data. It is proposed to classify chips under two different groups. The first group is characterized by the edge fracture that is accompanied by the fully developed shell-like chip with typical zones of the fracture crack propagation (traces of axisymmetric quasi-cone crack propagation). The second group of chips involves the edge fracture without smoothly outlined borders of the fracture crack propagation on the lateral surface of the specimen with a set of branched and randomly oriented cracks having the reflecting zone of comparatively small dimensions. The mechanisms of variation in the shape of chip scars (fracture crack propagation trajectory) are implied with the increase of the fracture load on the indenter or fracture distance. It is established that the fracture resistance is invariant to the fracture load and does not depend on the asymmetry of chip scars according to their side views. The authors demonstrate the correlation dependence between the test results (the S+EF and SEVNB methods) on the different glass types, which reveals the effect on the specified cracking and chipping of the material in the zone of its contact with indenter for fracture resistance of glass under local edge loading. The authors propose to use the methods of indenter scratching of the specimen surface till its edge chipping as the rapid assessment of damage and fracture resistance of glass in the solution to the optimization tasks, certification procedure or materials' selection. [ABSTRACT FROM AUTHOR]

A theoretical study of Mode II fracture in functionally graded beams was carried out. A beam configuration with two symmetric longitudinal cracks was suggested in order to generate Mode II loading conditions. The beam mechanical behavior was described by nonlinear stress-strain relation. The fracture behavior was analyzed by applying the J-integral approach. Closed form analytical solutions were derived of the J-integral for two laws for variation of the modulus of elasticity along the beam height. Nonlinear analyses of the strain energy release rate were performed by considering the energy balance in order to verify the J-integral solutions. The results obtained can be applied to optimize the functionally graded beam structure with respect to the Mode II fracture performance. Also, the analytical solutions derived are very convenient for parametric studies of nonlinear fracture behavior of functionally graded beams. The present paper contributes towards the development of nonlinear fracture mechanics of functionally graded materials. [ABSTRACT FROM AUTHOR]

The paper addresses an approach to the physical notion of failure of solids in the presence of an active medium (a destructive compound), which is based on two successive steps. The first one is to go from considering a body as an elastic or viscoelastic continuum to studying it as an atomic-molecular system. The second step that follows the investigation of the atomic structure is to take into account the influence of atomic motion in a solid during the study of mechanical properties of solids (at high temperatures, in a wide range of loading speeds, under cyclic and vibrational loads), which is based on the experimental data on ultimate strength and yield stress of metals. A mechanism of crack initiation in a loaded metal under the action of destructive compounds is discussed. The capillary and diffusional propagation of a molten liquid-metal compound along grain boundaries and structural defects in a solid metal in combination with the viscous flow of the melt over its surface are shown to dictate the crack propagation into metal structure. The pattern of the affecting destructive factor has been clarified. [ABSTRACT FROM AUTHOR]

The paper presents methods for determining the elastic modulus, sound speed, logarithmic decrement of vibrations (internal friction), tensile, compressive and bending strength, crack resistance, specific work of fracture of small-sized specimens. The specimens of polycrystals of superhard materials, which are prepared in high-pressure apparatuses, or of other expensive sintered materials (boron carbide, silicon nitride, hard alloys), which have a high hardness and elastic modulus, have typically a small size. Most of such materials experience significant dynamic loads during operation in products (metal-cutting tools, armor protection elements). It has been shown that disk specimens of brittle materials 3-15 mm in size can be used to determine strength characteristics under dynamic loading. The use of such specimens makes it possible to avoid oscillations in the loading diagram and to reduce the measurement error of breaking load. Moreover, it is possible to determine on such specimens the specific work of fracture of brittle materials from energy balance in measuring bars. Methods for determining mechanical characteristics under dynamic loading using Hopkinson-Kolsky bars are described, and examples of using procedures for the investigation of hard alloys, polycrystals of superhard materials based on diamond and cubic boron nitride, boron carbide and silicon nitride, obtained by the Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine, are given. [ABSTRACT FROM AUTHOR]

The paper presents the results of low-cycle fatigue tests for 10GN2MFA steel obtained by martensitic melting and electroslag remelting in air and in heat transfer medium at both room and elevated temperatures, as well as cyclic crack growth resistance in high-temperature aqueous medium. It is shown that the method of steelmaking exerts a strong influence on the fatigue crack growth stage. [ABSTRACT FROM AUTHOR]

Fracture occurs at interface corners due to stress singularity which generates as a result of material discontinuity and geometrical configuration. In elastic stress field near a bimaterial notch tip, eigenvalues extracted from Airy’s stress function approach determine the order of singularity. In this paper, the characteristic equation of elastic stress field near bimaterial notches is investigated. The study is done on singular eigenvalues as well as the first non-singular eigenvalue which has not been well studied before. First, different combination of materials and geometrical configurations for two of the most applicable paths in the Bogy diagram (β = 0, β = α/4) were studied and the results were comprehensively discussed. It was shown that the geometrical and materials configurations near a bimaterial notch tip can significantly affect on the stress singularity near these corners. Finally, the areas between two lines β = 0 and β = α/4 in the Bogy diagram with high stress singularities were determined and discussed for both the first and second singular eigenvalue. [ABSTRACT FROM AUTHOR]

We describe the application of the dual boundary element method for the determination of stress intensity factors in plate bending problems. The loadings considered include internal pressure, and also combined bending and tension. Mixed mode stress intensity factors are evaluated by a crack surface displacement extrapolation technique and the J-integral technique. The boundary element results for the case studies considered in the paper have been compared with either analytical or finite element results and in all cases good agreement has been achieved. [ABSTRACT FROM AUTHOR]

The authors have outlined methodological principles and a procedure of performing the updated analysis of stress-strain state and fracture resistance of welded joints between coolant headers and PGV-1000M steam generator vessel. The paper gives the results of the elastic-plastic fracture resistance analysis of a welded joint containing variously shaped surface defects, in modeling a design operation cycle and an accident situation. According to the data obtained, the deformation loading history, residual technological stresses, and inclusion of surface damages have a significant effect on the design assessment of fracture resistance of a welding joint. It has been shown that the conventional linearly elastic calculation of fracture resistance of welded joints has an inadequate degree of conservatism and thus overestimates strength of the joints. [ABSTRACT FROM AUTHOR]

The paper considers procedures for predicting safe damage to compressor and turbine disks in stationary and aircraft gas turbine engines at the stage of subcritical crack growth. The methods are proposed to evaluate inspection intervals and amounts of routine maintenance with consideration of the regularities underlying this type of crack growth. In this case, the features in the operation of materials are taken into consideration for stationary (peaking, semi-peaking, and steady-state modes) and aircraft (typical flight cycles) gas turbine engines. The crack propagation near various stress concentrators is analyzed with the help of the developed program using a stationary gas turbine disk as an example, which allows one to predict the crack growth life of the disk and the most probable location of its failure. [ABSTRACT FROM AUTHOR]

The paper summarizes the results of approximate calculation of the influence of amplitudedependent damping capacity of a vibrating system on vibrodiagnostic parameters of the presence of a closing mode I edge crack in a cantilever beam of rectangular cross section for various methods of excitation of the second-order resonance in the lowest natural bending mode. [ABSTRACT FROM AUTHOR]

The paper addresses the main methods of predicting the temperature dependence of fracture toughness. The authors have analyzed a system of margins which have to be introduced in order to adequately and conservatively predict this dependence using the results of testing surveillance coupons. A methodology is put forward for determining a margin for spatial nonuniformity of properties of the reactor pressure vessel material, which is based on simultaneous deterministic and probabilistic calculations of brittle fracture resistance of a reactor pressure vessel. [ABSTRACT FROM AUTHOR]

The paper presents results of studies of the effect of electrodynamic treatment on the improvement of the fracture resistance of flat AMg6 aluminum alloy specimens under cyclic loading. It has been shown that the grip conditions of specimens to be treated have a considerable effect on the crack initiation resistance of the AMg6 alloy under symmetric loading cycle with amplitude close to the conventional yield strength of the metal. [ABSTRACT FROM AUTHOR]

The paper presents the results of the investigations into torsional vibrations of steam turbine shafting occurring during the connection of the turbine generator to the power system with the coarse synchronization. A strong dependence of these vibrations on the parameters of the reaction torque is shown. The fatigue damage of steam turbine shafting material is evaluated for different modes of connection of the turbine generator to the mains. [ABSTRACT FROM AUTHOR]

The paper considers the problems within an extensive research program addressing the crack propagation in flat and tubular specimens of brittle and plastic materials of different physical nature. Based on implementation of the program, the authors have elaborated scientific fundamentals for a new approach to fracture analysis of sheet metals and thin-wall structures. It is shown the task of high priority for formulating a practically acceptable transferability law is to obtain experimental data on evolution of the crack void geometry starting from the crack initiation and till the specimen breakdown. [ABSTRACT FROM AUTHOR]

The paper presents the results of approximate calculations of vibrodiagnostic parameters indicating the presence of a closing fatigue edge crack in bars with different boundary conditions versus the crack parameters and exciting load under subharmonic resonance in principal bending mode. [ABSTRACT FROM AUTHOR]

The paper addresses special features of nonlocalized and localized fatigue damage in metals and alloys. The sizes of maximum fatigue cracks at a fatigue limit in metals and alloys of various grain sizes and strengths are analyzed. The authors discuss the linear and nonlinear fracture mechanics criteria that relate the fatigue crack sizes and the fatigue limits. The experimental values of the fatigue crack size are compared to those calculated by different criteria. Special features of initiation of nonpropagating fatigue cracks in the presence of stress concentrators are studied. [ABSTRACT FROM AUTHOR]

This paper presents the results of investigations on the microcracking of composite ceramic materials, such as electrical engineering porcelain and silicon nitride ceramics, using the acoustic emission technique. The analytical expression describing the kinetics of microcrack accumulation is refined. The influence of the loading rate on the strength characteristics of ceramics and the special features of acoustic emission during their cracking are studied. The dependence of the total acoustic emission count on the stressed surface area of specimens is found. The notion of the microcracking modulus of ceramic composite materials is introduced and its mismatching with the Weibull modulus in strength tests of ceramics is shown. [ABSTRACT FROM AUTHOR]

The paper presents some findings of analytical and numerical investigations aimed at determining the influence of inelastic resistance on vibrodiagnostic parameters indicating the presence of damage, such as a breathing crack, in an elastic body under the main and subharmonic resonances. [ABSTRACT FROM AUTHOR]

This paper considers the basic principles of the most widespread methods for determining typical states of a mode I through crack in specimens and structures of sheet metals that are fractured under conditions close to the plane stress state. The results of experimental investigations are presented which make it possible to judge of the relative advantages and disadvantages of these methods from the standpoint of their possible use in engineering assessments of the integrity and remaining strength of thin-wall structures. [ABSTRACT FROM AUTHOR]

The objective of this paper is study the influence of the matrix swelling due to water on the damage of the fiber matrix interface of a composite material. The results obtained by a genetic approach based on Weibull probabilistic model, show good agreement between the simulation and the actual behavior of the two materials T300/914 and PEEK/APC2. Also the absorption of water by the matrix increases significantly the interface damage. [ABSTRACT FROM AUTHOR]

In contrast with modeling of the contraction joints, the performance and influence of lift joints are usually neglected in numerical analysis of concrete arch dams. In this paper, the seismic nonlinear response of a concrete arch dam-reservoir-foundation system is investigated with considering the effects of lift joints using orthotropic-based material. An anisotropic damage mechanics approach is introduced and modified to take into account the effects of weak horizontal planes between concrete lifts during the construction phase. This model is capable to consider the pre-softening behavior, the softening initiation criterion and anisotropic cracking behavior in mass concrete. The coupled equation of motion in dam-reservoir system is solved by staggered displacement method while the foundation rock is assumed as a mass-less and rigid mediums. The coupled system is excited using three-component ground motion in the maximum credible level. It is found that using orthotropic-based material increases crest displacements and also leads to more damage in the dam body in comparison with the case using the common isotropic-based material. [ABSTRACT FROM AUTHOR]

The paper provides some results of the investigation of the influence of stress state type on accumulation of dispersed damages in structural carbon steel sheet under repeated static biaxial tensile loading. It is shown that the lowest damage accumulation ability of the metal is observed under biaxial tension with a biaxiality index ranging between 0.25 and 0.3. [ABSTRACT FROM AUTHOR]

The paper addresses the well-known (from available publications) phenomenological strength criteria for anisotropic materials, which are most widely used in application software. [ABSTRACT FROM AUTHOR]

The paper presents results of experimental investigations to assess the effect of Mode I and II thermomechanical pre-loading on the crack resistance of specimens in four-point bending tests. Specimens were subjected to Mode I and II repeated loading. The investigations were carried out on heat-resistant reactor steels. An algorithm for the numerical assessment of fracture toughness with allowance for thermomechanical pre-loading under mixed loading conditions is proposed. [ABSTRACT FROM AUTHOR]

The paper addresses the influence of high-temperature ultrasonic treatment on the structure and impact toughness of steel 15Kh2NMFA. The observed increase of impact toughness and decrease of ductile-brittle transition temperature for the steel upon ultrasonic treatment of various durations are due to the formation of a uniform defect structure. [ABSTRACT FROM AUTHOR]

The paper addresses damage accumulation processes that occur during static deformation in steels 45 and 09G2S and in brass L63 in the initial state and upon 'grain annealing.' The authors discuss new experimental evidence on the damage accumulation kinetics during deformation of polycrystalline materials that differ in nature and grain size, including materials in the unloaded state and those under stresses, with small and very small strains (0.05-0.15%). The results obtained have been the necessary physically consistent explanations. Analytical approximations of the correlation between the main mechanical properties of materials (hardness, yield stress, and ultimate strength) and their structure parameters (grain size) are given. [ABSTRACT FROM AUTHOR]

The paper addresses the dependence of acoustic emission produced in rolled hafnium GFÉ-1 under tensile deformation on the material's structural state. A correlation has been established between the material structure, the level of mechanical properties and the values of acoustic parameters. Acoustic emission in non-recrystallized hafnium under tensile deformation is recorded only at the stages that precede fracture. Upon recrystallization annealing at temperatures of 1123 and 1373 K acoustic emission occurs at all the stages of tensile deformation. The highest level of acoustic emission activity in hafnium is observed during the transition from elastic to elastic-plastic strain. [ABSTRACT FROM AUTHOR]

new procedure for computing the J-integral for FEM discrete models, which is based on the use of magnitudes of nodal reactions and displacements, has been implemented. The paper presents theoretical substantiation and practical evidence that confirm the invariance of the J-integral values found by this procedure for the case of cracks of Mode I and mixed fracture mode. A three-dimensional elastic-plastic deformation problem for a compact specimen has been solved. [ABSTRACT FROM AUTHOR]

For a reactor pressure vessel steel 15Kh2MFA(III) experiments and calculations have been carried out to study the factors that have an influence on the increase of the lower-shelf fracture toughness in the temperature dependence diagrams upon warm prestressing. Stereoscopic fractography and numerical investigation have demonstrated that after the warm prestressing the crack tip remains blunt. This reduces the stress singularity during subsequent loading and raises the material fracture toughness. The paper gives the calculated data on residual stresses and crack-tip opening displacement during warm prestressing and upon relief. The calculated results are shown to agree well with the known analytical relations and experimental data. [ABSTRACT FROM AUTHOR]

We review the currently available approaches, applicable codes and standards for assessment of defects in trunk pipelines and discuss advantages and disadvantages of the National pipeline regulations. The paper outlines the main principles of the newly introduced normative document that regulates the assessment of strength and remaining life of pipelines containing service defects. [ABSTRACT FROM AUTHOR]

The paper addresses the use of small-sized specimens of various types, including those with deep (50%) side grooves, for the purpose of fracture toughness prediction. The experimental data for numerous (more than 500) small-sized specimens prepared from materials of various degrees of embrittlement are compared to the test results for full-sized specimens of C(T) type. The concepts of Master Curve and Unified Curve are applied for the processing of experimental data. To handle the test results for small-sized deep-grooved specimens a calculation procedure has been elaborated, which adjusts the calculation method specified in the ASTM Standard E 1921. We provide recommendations of how to use precracked Charpy type deep-grooved (50%) specimens for prediction of a representative temperature dependence of fracture toughness. [ABSTRACT FROM AUTHOR]

The paper gives the research findings which make it possible to construct an algorithm for the residual life assessment within the framework of a tensor approach to describing damage in a material under inelastic deformation. The authors propose explicit finite criterial relationships for the residual life assessment, which extend the known relationships to cover a wider range of loading processes. [ABSTRACT FROM AUTHOR]

The paper considers methods of accelerated determination of endurance limits of metals and alloys based on the analysis of regularities in their inelastic deformation, strain and energy criteria of fatigue fracture, and methods for life prediction with the use of those criteria. [ABSTRACT FROM AUTHOR]

The paper discusses the available analytical methods and the results of investigation of vibrations of elastic bodies with a bilinear asymmetric characteristic of restoring force that simulates the behavior of a local discontinuity in a material in the form of a closing fatigue crack. An approximate analytical method is put forward for the determination of vibrodiagnostic parameters of the vibration process of the nonlinear system under study in the range of weak superharmonic resonances. [ABSTRACT FROM AUTHOR]

The paper covers the experimental study of the influence of cycling frequency ranging from 20 Hz to 10 kHz and the cycle asymmetry on the crack growth resistance of VNS-25 stainless steel. It is demonstrated that as the cycling frequency is raised, the crack growth rate decreases monotonically, while threshold values of the stress intensity factor $\backslash DELTA\; K\_th$ grow. The latter is due to the fact that at high cycling frequencies the plastic deformation processes remain incomplete and the contribution of the fracture mechanisms that facilitate greater energy intensity of fatigue crack growth processes becomes more significant. A comparison of $\backslash DELTA\; K\_th$ and fatigue life values as a function of cycling frequency for smooth and notched specimens demonstrates that if represented in relative coordinates these functions are described by a common relationship. This allows a quantitative assessment of the effect of the strain cycling rate on the above-mentioned properties of a material from the results of tests of one type only. It has been found that the values $\backslash DELTA\; K\_th$ in asymmetrical loading cycles are related to those in symmetrical cycles, as well as to a coefficient of material's sensitivity to the static component, and linearly depend on the load ratio. [ABSTRACT FROM AUTHOR]

This study proposed a model describing the kinetics of short fatigue crack growth from a smooth surface and from the top of a blunt notch. The driving force of the fatigue crack is the effective stress intensity factor (SIF), which is defined as the difference between the applied "external" and "internal" SIFs, characterizing the material resistance to crack growth. The model makes it possible to calculate the kinetic diagram of the growth rate of a short fatigue crack from the notch and estimate the fatigue life (number of load cycles) from the moment of crack initiation until it reaches a certain size at a constant range of applied nominal stresses. The total fatigue life is divided into the crack initiation stage (stage 1) and crack growth stage (stage 2). In addition to the load parameters and notch's geometric dimensions, the input data for the calculation are the static strength characteristics (elastic modulus, Poisson's ratio, and macroyield initiation stress) determined via short-term tensile tests of standard specimens of this material, and microstructural characteristics (grain size, grain misorientation angle, Taylor's factor, and Burgers vector) determined from the microstructural analysis of the initial material. The calculations based on the proposed model of the kinetic curve of the crack growth rate and total fatigue life of the tested specimens made of steel 45 show good agreement with the experimental ones. [ABSTRACT FROM AUTHOR]

The effects of the dip angles of the echelon notches on the acoustic emission (AE) are studied under uniaxial compression. For this comprehensive analysis, discrete-element simulations are used. Therefore, model dimensions of 150×150 mm were specially prepared. These models contained three echelon cracks with different lengths of 4.5, 3, and 1.5 cm, and a 2 mm vertical distance between the cracks. The inclination angles of the middle crack varied as 0°, 15°, 30°, 60°, 75°, and 90° in the specimens containing echelon cracks with different configurations. Two neighboring cracks were perpendicular to the middle cracks. Twelve different models were designed and tested under uniaxial compression. It was observed that the failure process and crack propagation patterns in the rock-like material specimens were affected by changes in cracks' angles and their configurations. The AE events in the loaded specimens grew rapidly during the initial loading phase. Numerous AE events showed a decline in the induced stresses at the peak load states. [ABSTRACT FROM AUTHOR]

A methodology for theoretically estimating the endurance limit of a material for conditions of multicycle fatigue is proposed. The estimation is based on the fact that under these conditions, a nonpropagating surface fatigue crack of one grain size exists at the level of the applied stress range equal to the endurance limit. In this regard, the tools of linear-elastic fracture mechanics were used in the development of the methodology, but with corrections for the size and geometry of a short fatigue crack. The methodology allows for estimating the endurance limit of smooth specimens under symmetric and positive stress ratios of the loading cycle. The initial data for the estimation are the characteristics of the static strength and microstructure of the material. The reliability of the proposed estimation is confirmed by experimental fatigue data for structural alloys of various classes taken from the literature. [ABSTRACT FROM AUTHOR]

The stress corrosion cracking (SCC) crack propagation behavior of nuclear power structural materials in a high temperature water environment can be regarded as oxide film rupture and regeneration under the interaction of material, corrosive environment, and mechanical micro- environment. To understand the influence of the passivation process of the shape around the crack tip over time on the creep field, the change of oxide film curvature value is used to represent the passivation process of the shape around the crack tip. The finite element software ABAQUS is used to simulate and analyze the crack tip creep field and its distribution law of the oxide film at the crack tip under different curvatures. Results show that different oxide film curvatures will affect the size and distribution of stress and strain around the crack tip. With the increase of oxide film curvature, the creep amount, creep rate, and crack growth rate of the base metal all show an increasing trend. [ABSTRACT FROM AUTHOR]