Search

The present paper summarizes some recent experimental, theoretical and numerical results on brittle fracture of isostatic polycrystalline graphite. The analyses have been carried out on V-notched samples under mixed mode (I+II), torsion and compression loading, considering various combinations of the notch tip radius, opening angle and notch tilt angle. The static strength of the considered specimens is assessed through an approach based on the strain energy density averaged over a control volume. The center of the control volume is located on the notch edge, where the principal stress reaches its maximum value. The correct orientation is obtained by a rigid rotation of the crescent-shaped volume while the size depends on the fracture toughness and the ultimate strength of the material. This methodology has been already used in the literature to analyze U- and V-shaped notches subject to mode I loading with very good results and advantages with respect to classic approaches. The results reported in this new work show, also under mixed mode loading conditions, a good agreement between experimental data and theoretical predictions. [ABSTRACT FROM AUTHOR]

The paper summarizes the findings of a study of the influence of stiffness parameters of an elastic restraint in a damaged regular system consisting of two duplicate elements and modeling a two-blade assembly, on the generation of vibration of the system under fundamental resonance. A discrete dual-mass model whose vibration is described by a nonlinear set of differential equations of second order has been chosen as a design model of the structurally regular system under consideration. Numerical investigations have been performed using the Runge-Kutta method to solve a nonlinear set of differential equations and the fast Fourier transform method to process the solutions obtained. The dependences of the resonant frequency ratios and resonant amplitude ratios of the first-harmonic vibration on the damage parameter have been derived for the discrete model of the regular system in inphase and antiphase modes, with different parameters of the elastic restraint for the damaged subsystem and for the intact one. It is demonstrated that with a preset value of the damage parameter the frequencies of the inphase and antiphase modes grow with increasing coefficient of the elastic restraint of the subsystems. This influence is the most significant in the case of the antiphase mode of vibration of the subsystems. The elastic restraint coefficient has also a substantial effect on the level of resonant amplitudes of the first-harmonic vibration for the regular-system model under study. It has been found out that as the elastic restraint coefficient grows the resonant amplitude of the intact subsystem increases under the inphase-mode vibration and decreases under the antiphase one. The values of the resonant amplitudes of vibration of the damaged subsystem are influenced by the coefficient to a lesser extent. The maximum value of the resonant amplitudes of vibration of the damaged subsystem is almost independent of the elastic restraint coefficient. [ABSTRACT FROM AUTHOR]

The paper considers the processes related to the specimens and loading device in the tensile testing of metals in strain-controlled mode, including under the conditions of cryogenic temperatures up to 4.2 K. It is demonstrated how the potential elastic energy accumulation and its subsequent relaxation in the development of the specimen strain affect the process of kinetics. The strain rate dependencies on the strain value and stiffness factor (relation between the values of stiffness of the specimen and the machine) are obtained. Noteworthy is that the values of initial and nominal strain rates can differ by an order of magnitude in case of the machine compliance. To obtain the strain rates that are similar for different machines at the initial stage of the process, the formula is proposed allowing one to calculate the required nominal rate. At the temperatures lower than 30 K there is a dramatic increase of the influence of the machine stiffness, dimensions and shape of the specimens on the obtained characteristics, which requires the special measures in the process of testing. Some international and national standards are considered. It is shown that, at present, the process of standardization for tensile testing of metals is inadequate, and the requirements of the current regulatory documents are the minimum, which are not in agreement with the development paces of testing equipment. To significantly enhance the level of accuracy of the obtained mechanical characteristics, it is required to employ the urgent measures as the machine compliance limitation, as well as the decrease of the dimensions range for the specimens together with the standardization of the permissible range of the stiffness factor, and the required selection of the nominal strain rate considering the latter. [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]

An exact solution for the problem of vibration of a circular plate weakened along an internal concentric circle due to the presence of an angular crack, rotationally restrained and simply supported along an edge of the plate is derived. Frequencies for the first six modes of plate vibrations are computed for varying values of the elastic rotational edge restraint, radius of an angular crack and the extent of weakening duly simulated by considering an angular crack as an elastic rotational restraint on the plate. Internal weakening due to crack is found to cause decrease in fundamental frequency of the plate by around as high as 30%. Exact method of solution and the results presented in this paper are expected to be of specific use in analyzing the effect of an angular crack on fundamental frequency of the circular plate in the presence of a rotational restraint with simply supported boundary along the outer edge of the plate. These exact solutions can be of use in checking numerical or approximate results obtained through numerical methods such as finite element method. [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]

A new quadratic strength criterion for an orthotropic material is put forward. It is based on the data of 21 simplest experiments in uniaxial tension, compression, and pure shear. The number of independent tests to failure is shown to be reduced to ten in the case of a unidirectionally reinforced (transtropic) composite. The paper addresses also some of the other types of symmetry of elastic and strength properties, which are frequently encountered in practice. [ABSTRACT FROM AUTHOR]

The paper presents the results of study of fatigue and inelasticity of 08Kh18N12T austenitic steel under single-and two-frequency loading prior to and after operation for 100,000 hours as a material of WWER-440 reactor coolant piping. The results obtained are discussed. [ABSTRACT FROM AUTHOR]

The paper discusses an approximate analytical method for the calculation of vibrodiagnostic parameters of an elastic body with a closing crack, which is modeled by an elastic system with a single degree of freedom at a bilinear asymmetric characteristic of the restoring force, in the region of a weak 1/2-order subharmonic resonance. [ABSTRACT FROM AUTHOR]

The effect of the geometric shape of eroding particles on the threshold rate of failure has been assessed. It has been shown that when the eroding particle size is changed, the failure mode may change from brittle to ductile and vice versa. The paper presents the results of a comparative analysis of the erosion resistance of some metallic materials, using a structural-time criterion of failure, for the impact of a single abrasive particle of cylindrical shape on the surface of an elastic half-space. Hertz’s classical theory of impact is used. [ABSTRACT FROM AUTHOR]

The paper considers a plane stability problem of thin-walled bar of angular profile made of an isotropic linearly elastic material. The critical parameters were determined with the aid of the second version of three-dimensional linearized stability theory and the ground state from equations of the linear theory of elasticity. The approximate solution of the stability problem was sought by the net method. The dependence of the critical parameters on the thin-walledness parameter of structure has been examined, and the errors of the applied stability theory, which is used for the design of frameworks, have been determined. [ABSTRACT FROM AUTHOR]

The paper covers an experimental study of the laws that govern the variation of yield limit and stress-relaxation limit as a function of stress amplitude and plastic strain in Grade 45 steel and D16T alloy under the conditions of preliminary static and cyclic tension including strain aging. The mechanical characteristics of these materials are shown to grow with increasing plastic strain irrespective of the loading type but decrease with increasing stress amplitude. It has been found that as a certain level of plastic strain is achieved the stress-relaxation levels in the materials become the same irrespective of the type of pre-loading. [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 results of computational experiments to determine the influence of the width and location of a groove as a model of open edge crack on the formation of the spectrum of natural frequencies of torsional vibrations of cantilever rods are presented. The modal characteristics of rods with geometrical parameters corresponding to a wide slenderness range of turbomachine rotor blades are considered. A modal analysis of rods with local material discontinuity in the form of a groove was carried out by means of three-dimensional finite element modeling. Based on the results of computational studies, the dependence of the change in the natural frequency of the 1st–4th torsional vibration modes on the location and depth of a 1 mm wide groove was determined. It is shown that under torsional vibrations at a certain location of the damage, the natural frequency of the rod is equal to the frequency without it. It was established that this relative location, called the transition point, is inherent in all modes of torsional vibrations of the objects under study. A characteristic feature is that the transition point depends on the depth of damage and the radius of inertia of the rod cross-section and does not depend on the rod length. It is shown that, in addition to the presence of a transition point, the obtained plots for the 2nd–4th modes of torsional vibrations are characterized by the presence of ranges of the relative location of the groove, at which there is exceeding the value of the vibration frequency of the undamaged rod which is caused by the ratio of its elastic and inertial properties. A comparative analysis of the laws governing the formation of the spectra of natural frequencies of torsional and bending vibrations of the rods under study in the fundamental mode and higher modes was carried out. These plots can be used to select a method for the vibration diagnostics of highly stressed parts of modern machines, in particular, turbomachine blades. [ABSTRACT FROM AUTHOR]

The stress-strain state of a drill string during its compression in a horizontal borehole is considered. The function of the elastic axis of the drill string as a wave curve is obtained, which enables one to improve the analytical models: evaluation of decrease of axial force depending on the drill string elastic axis shape, determination of the force of pressing of the string to borehole walls, and calculation of normal stresses in the cross section of drill pipes. [ABSTRACT FROM AUTHOR]

The paper considers interrelation between the regularities in the fatigue fracture and inelastic deformation taking into account the material properties, stress gradient and concentration, specimen size, load cycle asymmetry, complex stress state, temperature, loading frequency and conditions, scatter of the test results. Analysis of the data from the literature and results of original investigations has shown that the characteristics of inelasticity, which define nonlocalized fatigue damage, can be used in studies of general regularities of the high-cycle fatigue fracture. Specific results of such analysis are presented. [ABSTRACT FROM AUTHOR]

The singularities of the solution of the dynamic problems of elasticity theory in the vicinity of the normal section (at a right angle) of the perfect contact surface between two anisotropic media with free boundaries (ends) have been numerically studied. A two-layer cylinder of rather short length with free ends under an internal central axisymmetric blast load is considered. The calculations were made using an application package developed by the author with co-authors at the Pisarenko Institute of Problems of Strength of the National Academy of Sciences of Ukraine. Three cases of varying the layers (inner layer – outer layer) have been studied: isotropic steel–isotropic composite; isotropic steel–spirally transtropic (reinforced) composite, and reinforced composite–reinforced composite if both layers are made of the same transtropic material, but with different angles of spiral reinforcement (winding of fibers). It is shown that in all three cases, the zones where the contact reaches a free end will be singular. The index (degree) singularity for static and dynamic problems is the same. The degree of singularity increases with the relative difference in the stiffness characteristics of the layers. In the case of spirally reinforced composite layers, the degree of singularity depends largely on the angles of their reinforcement. Singularity can exist even under the contact of layers of the same anisotropic composite, but with different directions of the principal anisotropy axes (angles of reinforcement). For isotropic contacting layers, the singularity index in dynamics coincides with the exact one, obtained by the author earlier analytically in statics. [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]

A molecular structural mechanics approach is used to study the effect of double-atom vacancy defects (DAVD) on the elastic properties of zigzag and armchair single-layered graphene sheets (SLGS). To this end, the space frame structure is also adopted to model the interatomic forces of the C-C bonds. The numerical simulation results obtained via the finite element method strongly suggest that double-atom vacancy defects reduce the elastic module of SLGS, which effect weakens with graphene size. Finally, the elastic modulus and Poisson's ratio of SLGS are found to decrease with the number of DAVDs. [ABSTRACT FROM AUTHOR]

Within the framework of transversally isotropic body, the possibilities of describing the elasticity characteristics and load-bearing capacity of unidirectional carbon-reinforced polymer composites at high temperatures are analyzed. The dependences of the elasticity characteristics and strength parameters of the composite on the heating temperature and rate are established. The models for calculation of strength characteristics of ablating composite in cases of tensile or compressive loads codirected with the reinforcement axis are developed and discussed. [ABSTRACT FROM AUTHOR]

Results of experimental room-temperature studies on the deformation and strength of UOL-300-1A and UT-900-3A carbon cloth-reinforced plastics and laminar composites on their basis are presented. All elastic and strength characteristics of the materials are evaluated at the plane stress state. Evaluation lines for elastic and strength characteristics of laminar carbon cloth-reinforced composites are investigated. The prediction efficiency for elastic characteristics of laminar woven composites is analyzed on the basis of corresponding parameters of a single layer. [ABSTRACT FROM AUTHOR]

The amplitude parameters of the statistical characteristics of inelasticity of the surface layer of steel Kh18N10T, which describe the kinetics of inelastic strain accumulation of the material structure under consideration at high-cycle fatigue, have been obtained. The features of variation of the statistical characteristics parameters of inelastic strains of the surface layer of the material specimen have been determined. [ABSTRACT FROM AUTHOR]

The presented research results imply a certain relationship between elastic and plastic parts of strain. Based on the preliminary summary of this relationship, a new strength criterion is proposed, which can be treated as modification of the maximum principal strain criterion. Since the proposed approach establishes a relationship between strength and yield criteria, it can also be treated as a new yield criterion. [ABSTRACT FROM AUTHOR]

Within the context of the nonclassical model of composite beams the analytical solution has been obtained for a beam having a longitudinal section collinear to its median line. Bending load on the beam facilitates opening of the section. The elementary formulas for stress and displacement within all parts of the beam have been obtained. The accuracy of results is confirmed by their comparison with the corresponding data obtained in the solution of plane problem of the theory of elasticity using the boundary element method. [ABSTRACT FROM AUTHOR]

The most common methods for determination of mechanical characteristics of composite materials are considered. The accuracy of methods for each constant of some unidirectional composite materials based on E-glass fibers and epoxy binder is found. [ABSTRACT FROM AUTHOR]

A model and method for investigation of the vibrations of a multi-disk rotor on two nonlinear supports with ball bearings are developed. This model considers the gyroscopic moments acting on disks and elastic properties of the shaft. The vibrations are studied using the Shaw-Pierre nonlinear normal modes. Skeleton curves describing the rotor vibrations are analyzed. [ABSTRACT FROM AUTHOR]

A procedure for the creep analysis of diaphragms is proposed that is based on the multi-grid finite element method, Rabotnov-type creep aging theory and the method of variable parameters of elasticity. Three-dimensional calculation models of the diaphragm are constructed and the peculiarities of its stress-strain state are found taking into account the reduced resistance to creep in welded joints. It is shown that the axial displacements of the joints of the diaphragm are 30% higher for the end guide vanes than those for the middle ones, while the stress intensity is twice as higher. The area of the elastic strain intensity maximum at the leading edge of the guide vanes moves, with consideration of creep, towards the welded joint area where their intensity reaches 2%. [ABSTRACT FROM AUTHOR]

The reliability of one of the simplest methods for calculating vibration parameters in the region of subharmonic resonance for an elastic body with a breathing crack, which is modeled by a single-degree-of-freedom system with a bilinear asymmetric characteristic of the restoring force is assessed. The method is based on the proposition that in a nonlinear system the subharmonic vibrations exist alongside with the fundamental forced ones and are the free vibrations maintained by a driving force. [ABSTRACT FROM AUTHOR]

Elastic buckling, which occurs in shell structures, is a major design issue because it can cause failures of structures. In particular, the variation in buckling load caused by a decrease in the thickness of the walls of structures is a key issue for safe design. The arc-length method, which is a finite element method, is generally applied to solve this type of problem. However, it has been reported that there are some cases in which the path of the buckling load cannot be solved using this method. We verified the problem by applying the arc-length method to elastic buckling that occurs in a shallow partial spherical shell. To solve the problem, we formulated a novel algorithm used in the explicit finite element method for estimating minimum strength of thin-walled structures. In this algorithm, initial deformation is given by pressing a rigid wall to the vertical direction of buckling mode. We anticipate that the proposed method will prove to be a practical way of calculating the minimum load for partial elastic buckling that occurs in a general shell structure under pressure. [ABSTRACT FROM AUTHOR]

The analytical models based on micromechanical properties of composites are applied to predict the behavior of unidirectional (UD) composite under different types of loadings at room temperature and -60°C. In this study, unlike conventional methods which characterize UD composite via experimental tests on UD specimens under tensile, compressive and shear loadings, micromechanical properties of glass fiber and epoxy matrix at room temperature and -60°C are measured. Then by using various analytical models four elastic moduli and strengths at room temperature and -60°C are calculated. To investigate the validity of the results, experimental tests are performed and compared with analytical results. Results show that elasticity model is the best analytical method to predict four elastic moduli at room temperature and -60°C. Good fits are also found between experimental and analytical results for composite mechanical properties at the room temperature and -60°C. [ABSTRACT FROM AUTHOR]

Cyclic deformation behavior of metals and alloys under high-cycle loading in the nonuniform stress state is considered. A significant effect of the stress gradient on the cyclic inelastic deformation of the metal surface layers is shown. A model explaining the difference between the fatigue limits in the uniform and nonuniform stress states is proposed, which is based on accounting for the distinctions between cyclic stress-strain diagrams in the uniform and nonuniform stress states and for the fact that the fatigue limit is equal to the cyclic elasticity limit found for inelastic deformation typical of this class of materials. [ABSTRACT FROM AUTHOR]

procedure for the determination of stress intensity factors of 3D flat cracks is proposed, which uses integral identities for displacements and strains on the crack surface. New formulations of boundary problems of the mathematical theory of linear fracture mechanics have been obtained, which are used to develop finite element models. The unknown functions are nodal displacements on the crack surface. The data given are compared with analytical solutions and results obtained by other methods. [ABSTRACT FROM AUTHOR]

We present a method for refining the parameters of the model for nonlocalized damage accumulation in the steel 20 under static deformation, which are determined by variation in elastic modulus and degree of homogeneity of the material, that corresponds to the scatter of hardness characteristics during mass measurements at different stages of repeated static loading. [ABSTRACT FROM AUTHOR]

Based on the review of the available publications and the findings of the original studies, the author demonstrates that with cyclic stresses in the maximum-stressed surface layer being equal the inelastic strains in the presence of stress gradients are smaller than those in the material under uniform stressed state. As a result, there is a difference in the cyclic stress-strain diagrams between these cases. An equation for the cyclic stress-strain diagram is put forward, which allows for the stress gradient effect. A model is substantiated, which provides an explanation for the difference between fatigue strength characteristics under uniform and nonuniform stressed states. [ABSTRACT FROM AUTHOR]

We present basic principles of reliability calculations for steel underground pipelines resting on stochastic elastic foundation that based on the strength and stiffness criteria using the absolute maxima of arbitrary functions. Specific numerical examples illustrating a general calculation procedure are presented. [ABSTRACT FROM AUTHOR]

We consider different methods of modeling impact in vibroimpact systems by contact interaction force which can be regarded as elastic force as well as force corresponding to the Hertz law and with the help of the boundary condition method by using the coefficient of restitution. Comparison of the results of the modeling by means of these methods is performed, and recommendations for their application are proposed. [ABSTRACT FROM AUTHOR]

To obtain the complete solutions describing the balance of a reinforced concrete structure, it is necessary to introduce a behavioral law characterizing the physical properties of material. The goal of this work is to study the response of reinforced concrete elements by taking into account the variation of the shear retention parameter (aggregate interlock) and the mesh density. The concrete was assumed as elastic-plastic material and follow the Drucker–Prager failure criterion with associated flow rule, the steel reinforcements were assumed to be elastic-perfectly plastic. The numerical results obtained are compared with other results available in the literature. [ABSTRACT FROM AUTHOR]

We consider mixed variational formulations and the application of the mixed approximations of the finite element method to the solution of problems on natural vibrations of elastic bodies. To solve the generalized spectral problem, three forms of the mixed variational formulations are proposed. The correctness and stability of mixed variational formulations for displacements, strains and stresses are investigated. Matrix equations of the mixed method are given whose solution is performed using the modified algorithm of the steepest descent method. The results of calculations for natural frequencies of free vibrations of a straight and a circular beam are presented that are obtained in the solution of the problem in a two-dimensional formulation based on the classical and mixed finite-element method approaches. [ABSTRACT FROM AUTHOR]

Bulk metallic glasses have a very high corrosion resistance and mechanical strength. Bulk metallic glasses show elastic-perfectly plastic behavior with an extended region of elastic strain (≈ 2%). But at room temperature their macroscopic plasticity is weak even though a local plastic strain is observed in shear bands. A relaxation analysis allowed studying micro-mechanisms of plastic deformation and estimating the apparent activation volume (≈ 2000 Å3). [ABSTRACT FROM AUTHOR]

We analyze the problem of the stress distribution in an elastic orthotropic medium with an arbitrarily oriented elliptical crack. To construct the problem solution, the Willis approach is used which is based on the triple Fourier transformation of spatial variables and Fourier-image of Green’s function for an infinite anisotropic space. The investigation results in special cases are compared with the data of other authors. The effect of the elliptical crack orientation in an orthotropic space on the distribution of the stress intensity factors along its contour is studied. [ABSTRACT FROM AUTHOR]

The regularities of the scatter in the characteristics of fatigue and inelasticity of steels 45 and 1Kh13 have been studied under steady-state, step, and block loading. It is shown that the use of the inelastic strain per cycle as a measure of the fatigue damage accumulation rate makes it possible to take into account the scatter in the number of cycles to fracture and in the fatigue limits and to substantiate the cumulative fatigue damage rule. [ABSTRACT FROM AUTHOR]

Based on equations of linear three-dimensional elasticity theory, a problem is stated for the design calculation for rotating disks with hardening coatings, allowing for boundary layers formed. A numerical integration method is proposed for the stated problem, and some particular calculations are performed. Discussion of the calculated stress fields in the disk base material and coatings provides an explanation of some effects revealed, such as a significant improvement of load-carrying capacity of disks when face-coated with high-modulus layers of about 0.1–0.6 mm in thickness and a deterioration of this parameter (in some cases) when thicker coatings are applied. The authors study the applicability range of the conventional theory of disk strength calculation which assumes a two-dimensional stressed state and no boundary layers. [ABSTRACT FROM AUTHOR]

We discuss the theory and approximate methods for solving boundary-value problems of thermoplasticity in a quasi-static formulation when the process of non-isothermal elastoplastic deformation of a body is a sequence of equilibrium states. In this case, the stress-strain state depends on the loading history, and the process of inelastic deformation is to be observed over the whole time interval being studied. The boundary-value problem is stated as a non-linear operator equation in the Hilbertian space. The conditions that provide the existence, uniqueness and continuous dependence of the generalized solution on the applied loads and initial strains are defined. A convergence of the methods of elastic solutions and variable elastic parameters is studied to solve the boundary-value problems describing the non-isothermal processes of active loading taking into account the initial strains dependent on the deformation history and heating. [ABSTRACT FROM AUTHOR]

Bending of elastic circular sandwich plate with light filler, which is on an elastic foundation, is considered. To describe the kinematics of plate bending that is nonsymmetric in sandwich thickness, broken normal hypotheses are accepted. The foundation reaction is described by the Winkler model. The load is local symmetrical. A set of equilibrium equations and their exact solution in displacements have been obtained. Numerical results for a metal-polymeric sandwich plate are given. [ABSTRACT FROM AUTHOR]

We propose a new scheme of mixed-mode problem solution based on the deformation theory of plasticity with a power-law hardening stress-strain response and on application of elastic and plastic mixity parameters. Depending on the mixed-mode loading conditions and the initial crack line direction, this approach allows one to analyze a wide range of possible crack propagation paths controlled by shear and tensile mechanisms. The equilibrium equation with Airy function is used for a two-dimensional problem in the polar coordinate system. The Ramberg-Osgood model is applied to a material with power-law hardening behavior. Using the finite difference method we obtained a numerical solution of the mixed-mode loading problem with boundary conditions corresponding to two cases of crack propagation. Within the framework of the proposed approach we estimated the dependencies between mixity parameters and various loading parameters and crack inclination angle for a range of strain hardening exponent values, which dependencies closely fit the experimental data. [ABSTRACT FROM AUTHOR]

Analysis of data presented in the literature and results of unique studies revealed that nonlocalized fatigue damage of metals and alloys, which manifests itself in the initiation and propagation of a large number of microcracks distributed arbitrarily in the bulk of the material, can be considered with the use of the characteristics of inelastic deformation such as inelastic strain and inelastic strain energy per cycle. The author studied the nature of the material inelasticity and methods of its investigation. Analysis has been made of the hysteresis loop shape, width, and area, as well as of the main regularities of inelastic deformation of metals and alloys. [ABSTRACT FROM AUTHOR]

A framework for damage mechanics of concrete is applied to simulate the nonlinear elastic deformation behavior of concrete using finite element method (FEM). A rather simple isotropic damage model containing essentially no adjustable parameters is shown to produce results in remarkably good agreement with sample experimental data: the damage law requires only the fracture energy to be defined completely. The model is achieved by introducing a damage surface that is similar to the yield function in the conventional theory of plasticity. A special form of damage surfaces is constructed to illustrate the application of the model. A new damage criterion, defined as an equivalent strain norm, is proposed, in order to take into consideration the asymmetric behavior of concrete. For verifying the FEM program including the model, deformations predicted by this model are compared with both the experimental ones for the concrete structural model and the ones calculated without application of the continuum damage mechanics. [ABSTRACT FROM AUTHOR]

In order to construct a plate theory for a thick transversely compressible sandwich plate with composite laminated face sheets, the author makes simplifying assumptions regarding distribution of transverse strain components in the thickness direction. It is assumed that the transverse strains, i.e., εxz, εyz, and εzzdo not vary in the thickness direction within the face sheets and the core, but can be different functions of the in-plane coordinates in different sublaminates (the face sheets and the core). An algorithm, which takes account of damage progression in dynamic problems, is incorporated into the computational scheme based on the geometrically nonlinear formulation, and is applied to failure analysis of a sandwich plate under ground impact. [ABSTRACT FROM AUTHOR]

Molecular-dynamic simulation of the process of stretching of chromium and niobium nanocrystals and chromium-niobium bicrystals was performed to a pair-potential approximation. The authors obtained and analyzed the dependences of the potential energy, the number of pair interactions, work of deformation, stress, reduction in the cross-sectional area, and Poisson’s ratio on the strain with various orientations of nanocrystals with respect to the tensile force. They calculated the characteristics of elasticity, yielding, and strength of nanocrystals. [ABSTRACT FROM AUTHOR]