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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]

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]

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]

Results of complex experimental investigations on the determination of energy characteristics of fracture propagation in Charpy specimens cut in three different directions during impact bending tests for heat-resistant 15Kh2NMFA steel are presented. Tests were conducted over a wide temperature range on an instrumented vertical coping equipped with a high-rate data logging system. According to the test results, load diagrams were obtained. Total strain and fracture energy and its components were determined: crack nucleation energy, ductile crack growth energy, brittle crack propagation energy, and ductile final rupture energy. The use of quantitative fractography methods made it possible to determine both the specific strain and fracture energies, their components, and the average propagation rates of brittle and ductile cracks in the specimens' material. Critical brittle fracture temperatures were determined by two methods. The cutting direction of specimens significantly influenced the fracture energy characteristics and crack propagation rates in the material, which might affect the accuracy of strength and resource estimation of the NPP first contour components. [ABSTRACT FROM AUTHOR]

A model to describe the kinetics of short fatigue crack growth from an obtuse stress raiser (notch) is proposed. The model makes it possible to calculate the kinetic diagram of short fatigue crack growth rate from a stress raiser and to estimate the number of loading cycles from the moment of crack initiation up to the moment when the crack reaches the specified size at a constant range of applied nominal stresses. Apart from the loading parameters and geometrical dimensions of the stress raiser, the input data for calculations are the static strength characteristics (elastic modulus, Poisson's ratio, and yield stress, which are determined from short-term tensile tests on standard specimens of the material) and microstructural characteristics (grain size, Taylor factor, and Buergers vector, which are determined from microstructural analysis of the initial material). Calculations according to the proposed model of kinetic curve of crack growth rate and number of loading cycles during its growth for tested 45 grade steel specimens exhibited a good agreement with the experimental results. [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]

Three-dimensional laser scanning is an advanced technique for fracture roughness measurements. The surface roughness of fractures (discontinuities) accurately measured is of practical importance for proper evaluation of the mechanical properties of a fractured rock material. It is also appropriate to perform a more systematic study on the effect of a sampling interval on the roughness measurement accuracy. This effect was investigated based on the 3D-point-cloud data of a fracture surface acquired with laser scanning. A series of 2D profiles corresponding to twelve directions were extracted from concentric circular sampling windows of different diameters. The roughness measurement accuracy is quantified by the three parameters, viz the mean square first derivative Z2 , structure function SF, and roughness profile index Rp. The sampling interval effect was investigated for its different values by analyzing the three parameters of different profiles. It was established that SF was very sensitive, while Z2 and Rp were less responsive to the sampling interval. It exerts a much weaker influence on the rock material fracture roughness in comparison with anisotropy. [ABSTRACT FROM AUTHOR]

Impact behavior related to crack initiation and growth of low carbon martensitic 3Mn–Si–Ni steel was investigated by instrumented impact Charpy V-notch tests. Load–displacement curves were acquired, so significant characteristic load parameters and impact absorbed energies in different fracture phases from 20~(−70)°C were determined. The ductile–brittle transition temperature (DBTT) was also investigated and the corresponding fractograph was obtained. The DBTT of the 3Mn–Si–Ni steel is −50°C. With the temperature decreased from 20 to −70°C, the maximum force Fm increases and the difference between the Fm and the crack stable propagation initial force Fiu decreases. Higher force was used to trigger the crack and tended to be brittle fracture at lower temperature, such as −50 and −70°C. Also once the crack initiated, it will extend rapidly until fracture when the tested steel serves at very low temperature, especially below −20°C. With the impact temperature decreasing to −70°C, the crack unstable growth final force Fa decreased to nearly zero and there isn't distinct secondary fiber area. [ABSTRACT FROM AUTHOR]

Tensile and fracture properties of X80 pipeline steel were studied in a mimic petrochemical environment. X80 pipeline steel specimens were firstly exposed to air or H2S corrosive medium. Then their tensile properties and δ-∆a resistance curves were obtained in experiments. The influence of H2S corrosion on the X80 pipeline steel's crack growth resistance curve, fracture toughness, and plastic work loss was analyzed. The comparison between the test results after two pretreatments indicates that there was no significant difference in the X80 pipeline steel's ultimate tensile strength before and after H2S corrosion. But fracture elongation, area reduction and fracture toughness varied greatly (a substantial decrease in elongation and reduction of area). The crack growth resistance curve of the specimen in air was obviously higher than the crack growth resistance curve of the corroded one. Under stable crack growth stage, the crack initiation toughness δ 0.2BL of the specimen in air was 0.732 mm, 2.02 times that of the corroded one (0.364 mm). In the case of similar crack growth ∆a, the plastic work required in the crack growing process (UP) of the specimen in air was 2.29 times that of the H2S-corroded specimen ( U P ' ). H2S corrosion resulted in a significant reduction of the fracture toughness of X80 pipeline steel. Hence, H2S corrosion should be avoided in the process of natural gas transportation by pipelines, so as to protect the pipeline steel from toughness degradation. [ABSTRACT FROM AUTHOR]

Delamination fracture behavior of the three-dimensional functionally graded multilayered crack lap shear (CLS) beam configuration was studied analytically in terms of the strain energy release rate with linear-elastic fracture mechanics methods. The CLS under consideration can consist of an arbitrary number of layers, each having different thickness and material properties. The material of each layer is functionally graded along its width, thickness, and length. A delamination crack is arbitrarily located along the beam height. The strain energy release rate was derived by analyzing its density in the beam cross section ahead and behind the crack front. It was additionally analyzed using the strain energy release rate was performed by using the beam strain energy for verification. The effect of the material gradient and crack location along the beam height on the delamination fracture behavior was evaluated. [ABSTRACT FROM AUTHOR]

The residual welding stresses deteriorate the welded joint lifetime, and they are the chief cause of brittle metal fracture, i.e., corrosion cracking. The development of efficient methods to reduce the welding stresses, which are noteworthy for low energy costs and ease of realization, is customary important for the modern welding production. One such method is the electrodynamic treatment (EDT) based on the electric current pulse passing through the welded joints at the instant of dynamic load application to it. In the optimization of the parameters it is appropriate to test the pulse electric current effect on the residual welding stresses. The procedure of investigation of the EDT electric pulse component effect on the stress state of AMg6 aluminum alloy welded joints is proposed. It is established that the electric current pulse passing through the welded joint metal enhances the EDT efficiency in reduction of residual welding stresses. It is shown that the electrodynamic effect initiates the plastic tensile strains in metal, their interaction with the plastic welding compressive strains reduces residual stresses in the welded joint. Here the electric current pulses passing increases the peak values of the plastic tensile strains, which results in the more efficient electrodynamic effect on the residual welding stresses decrease in AMg6 alloy. The results lend credence to the physical model describing the electroplastic effect on the welding joints’ stress state. [ABSTRACT FROM AUTHOR]

The friction and wear of an new material for the drill joint were compared with those of traditional wear-resistant belt materials using an SD-1 test rig against a 42Mn2V steel counterface under deep and ultra-deep well conditions. This provides recommendations as to the tribological application of the wear-resistant belt. The results obtained strongly indicate that the friction and wear of a polycrystalline diamond (PCD) composite are much lower than those of the traditional wear-resistant belt materials. Among those materials, the friction and wear behavior of a FeNiNb alloy are higher than those of a FeCrMnMo alloy. Of the three wear-resistant belt materials, the bilateral protection performance of a PCD composite is the best one. It is feasible to use this composite as the wear-resistant belt material in the drill joint for deep and ultra-deep wells. The dominant wear mechanism of the wear-resistant belt materials is the microcutting wear, accompanied by the adhesive one. In addition, the wear degree of the PCD composite is the least one. [ABSTRACT FROM AUTHOR]

The mechanical characteristics of epoxy nanocomposites with ultradisperse diamond particles as a filler are investigated. It is shown that the addition of the particles of ultradisperse diamond at a concentration of 0.05 part by weight (pt.wt.) per 100 pt.wt. of the epoxy binder, increases the most the bending strength and reduces residual stresses in the composite. Moreover, the elastic modulus of the composite material increases. The chemical activity of the nanofiller particle surface resulting in the enhancement of physical and mechanical properties in the cross-linking of epoxy-based composite materials is determined by IR-spectrum analysis. The fracture surfaces of nanocomposite materials were investigated using optical microscopy. Based on the analysis of the topology of fracture surfaces of nanocomposite materials, it was revealed that the structure is ordered, with no visible inclusions, which is indicative of the maximum degree of cross-linking of composite materials with a concentration of ultradisperse diamond of 0.05 pt.wt. A uniform stress distribution in the volume of the investigated materials is indicative of the thermodynamic equilibrium in systems after cross-linking. [ABSTRACT FROM AUTHOR]

The main goal of this research is to propose a failure criterion based on the linear elastic notch fracture mechanics (LENFM) for predicting tensile crack initiation from a blunt V-notch, encountering large plasticity at the notch vicinity. First, some most recently published experimental results on tensile failure of V-notched ductile aluminum plates are briefly described. Then, with the aim to avoid complex and time-consuming elastic-plastic analyses, the equivalent material concept (EMC) is employed together with a LENFM-based fracture criterion, namely the averaged strain energy density (ASED) criterion, for predicting the load-carrying capacity of the V-notched aluminum plates. A very good agreement is shown to exist between the experimental results and theoretical predictions of the EMC-ASED criterion. [ABSTRACT FROM AUTHOR]

The characteristics of the mode I and mode II cyclic crack resistance of model wheel steel are compared. The effect of heat treatment of test steel on its microstructure parameters, as well as strength and cyclic crack resistance characteristics, is studied. [ABSTRACT FROM AUTHOR]

The coaxing effect in fatigue refers to an increase in the fatigue strength of material imduced by prior cycling at a stress level below the fatigue limit. In this study, the coaxing effect of multi-level stresses in the fatigue process in the automotive drive shaft material 40Cr was investigated by applying three levels of stress amplitudes below the fatigue limit in different sequences prior to conducting the conventional constant amplitude fatigue test with standard round bar specimens. The existence of coaxing effect under multi-level stress with a load sequence effect was observed and confirmed by the results. The longest fatigue life is achieved through three levels of coaxing load with a step increase sequence, while a decrease sequence will result in the shortest fatigue life. The mechanisms of the coaxing effect which increased the fatigue life at the crack initiation and propagation stages were observed, through fracture morphology analysis, as the regulation of micropores, decreasing of pore density and the narrowed striation spacing. This finding is instrumental for extending the service life of mechanical components. [ABSTRACT FROM AUTHOR]

Fracture and stress-strain state (SSS) of significantly anisotropic composite cylinders have been analytically and numerically investigated under internal explosion. Four possible types of fracture have been determined, including spallation fracture. The features of wave the SSS and strength of thin- and thick-walled shells as well as the dependence of the maximum permissible critical mass of the charge on the cylinder thickness have been established. [ABSTRACT FROM AUTHOR]

The aim of the present research is twofold. Firstly, to provide a new set of experimental results regarding tensile brittle fracture in key-hole notches and secondly, to check the suitability of the local strain energy density (SED) criterion in predicting the test results. For this purpose, 21 fracture tests were conducted at room temperature on a new version of the well-known Brazilian disk specimen containing a central dumbbell-shaped slit with two key-ends (Key-BD specimen) made of PMMA. The experimentally obtained fracture loads were theoretically predicted for different notch radii by means of the local SED averaged over a specified control volume which embraces the notch edge. It was shown that the experimental results could be well predicted by means of the SED criterion. [ABSTRACT FROM AUTHOR]

Fiber-metal laminates (FMLs) composed of metal lamina and reinforcing fibers exhibit an improved crack growth resistance as compared to conventional aircraft materials. The crack resistance of a hybrid FML composite consisting of LY12M aluminum alloy lamina and prepreg layers of HS2 glass fibers and T700 carbon fibers has been experimentally investigated on tensile specimens at stress ratios R = - 1, 0.1, and 0.5. The crack growth rate data at positive stress ratios demonstrate a significant scatter and a large difference between specimen's back and front surfaces formed by 1-mm thick outer aluminum layers. This violation of the test standard requirements for metal materials in the performed FML tests presents a problem of determining a proper failure criterion for the engineering applications of FMLs. Based on the comparative analysis of FML crack resistance results obtained, some qualitative conclusions are drawn on solving this problem. [ABSTRACT FROM AUTHOR]

The fatigue crack growth in D16AT aluminum alloy specimens with multiple stress concentrators in the form of holes is investigated experimentally. A generalized kinetic fatigue crack growth curve is obtained and the Paris equation coefficients are determined for a great number of cracks. It is shown that a general linear, semi-logarithmic relationship exists between these coefficients for aluminum alloys D16AT, 2024-T3, and 7075-T6. The statistical description of the fatigue crack growth based on the Paris equation is specified by the distribution of the exponent m, which is log-normal for aluminum alloys whose numerical characteristics are common to all types of alloys. [ABSTRACT FROM AUTHOR]

A new approach to the calculation assessment of strength and deformation capacity of braided ropes of the core-sheath type made of multifilament polyamide yarns is presented. The proposed method, referred to as the 'rule of mixtures' in the mechanics of composite materials, allows the mechanical characteristics of the rope to be determined in terms of the known geometrical parameters of its components, with consideration of the interaction of constituent elements. The results of the experimental investigation show that the interaction of individual structural components of the rope during the stretching process strongly affects the strength and deformation capacity properties determined at fracture. With an increase in the rope diameter from 5 to 18 mm, the relative strength of the core (normalized to the total cross-sectional area of the fibers) decreases by 10%. The use of the rule of mixtures appears to be promising for assessing the strength of braided ropes with the core and sheath materials having different elastic moduli. [ABSTRACT FROM AUTHOR]

Fundamental concepts and equations of the thermoviscoplasticity (inelasticity) theory are examined. Material functions are chosen, the basic experiment and identification method for the material functions, closing the thermoviscoplasticity theory, are formulated. Thermoviscoplasticity theory potentials for describing deformation and fracture of structural steels and alloys at different cyclic thermomechanical loads are demonstrated. [ABSTRACT FROM AUTHOR]