Search

Based on the analytical solution, the paper focuses on the residual stress distribution in composite parts with layered or graded structures as they cool from a high production temperature to room temperature. The solution obtained is valid for the most part of a body whose length and width are significantly higher than its thickness, by assuming that a state of equal biaxial stress exists. Laminar and graded ZrB2–ZrO2 composites are two examples of a ceramic composite that are taken into consideration to perform a quantitative analysis. It is demonstrated that in the layered composite the residual stress distribution has a stepwise shape, in contrast with the smooth distribution in the linear graded composite. The solution is easily extended to any nonlinear spatial variations of compositions. The changes in the thermal expansion coefficient and in the biaxial modulus under changes of the content of constituents are needed to estimate the residual stress in the composite. [ABSTRACT FROM AUTHOR]

Additive technologies already make it possible to obtain products from various materials with a complex structure. The most promising additive technology for producing metal products with hardened surface layers is vacuum electron beam printing using wire filaments and powders. Due to the high labor content and cost of the printing modes adjustment for such materials, computer simulation is a promising way to determine their optimal structure, which ensures high efficiency under operating conditions. In this work, a three-dimensional numerical model of a tribotechnical composite based on bronze was built using the method of movable cellular automata, which has been successfully utilized for 20 years to solve such problems. The influence of the concentration of hardening inclusions in the surface layer of composites on the establishment of a steady friction, the dynamic behavior of the friction coefficient, and structure formation in the tribolayer during interaction has been numerically studied. [ABSTRACT FROM AUTHOR]

The lumbar spine is one the most important parts of the skeletal system. In this work, a three-dimensional model of the lumbar spine was developed for further numerical studying its mechanical behavior. The resulting model was validated, verified, and an analysis of speed sensitivity was performed. The conditions of uniaxial compression were simulated imitating a standing position. The obtained data on the intradiscal pressure are consistent with the experimental data given in the literature. [ABSTRACT FROM AUTHOR]

The properties of materials are determined by their structure. Because of the wide capabilities of novel technologies for the formation of complex multiscale structure of new materials, the ability of modern computational methods to describe and characterize such a structure completely is of particular interest. In this paper, a computational method for constructing a correlation function to describe a two-phase structure of the composite material was developed based on the analysis of two SEM images of its surface. It was shown that an analysis of the graphs of the correlation functions and their derivatives makes it possible to reveal the characteristic sizes of the structure for each of two phases. [ABSTRACT FROM AUTHOR]

Osteonecrosis of the femur head is a degenerative disease of the musculoskeletal system that has the most destructive effect on cancellous bone. Physiotherapy is used to improve the condition of biological tissues. One of the methods of external mechanical action, which has a therapeutic effect, is ultrasonic loading. In this work, a numerical model of ultrasonic impact on a healthy hip joint was developed based on the computational particle mechanics. Using computer simulation it was found that the conditions for the regeneration of bone tissues of the hip joint are created with ultrasonic wave with an intensity of more than 3 W/cm2. [ABSTRACT FROM AUTHOR]

In this paper, the model of elastic-plastic media in Drucker – Prager form was adapted for analysis of the stress state of the lithosphere. The Cratonic Jelly Sandwich model was used to define the cohesion and coefficient of internal friction dependences on depth. To test this adaptation, the mechanical behavior of deep geological structures was numerically analyzed. To create the computer structures of the researched region, the geological data of the "Shpat– 1983" profile was used. It is shown that plastic strain begins in the weak layers of the Earth's crust and upper mantle and progresses to the strong layers of the Earth's crust in the form of bands. [ABSTRACT FROM AUTHOR]

The disc replacement is used when the intervertebral discs are worn out, which is the result of degenerative diseases. In recent years, some extra attention has been paid to implant materials. In this work, models describing the mechanical behaviour of the material of the M6-L endoprosthesis were developed. The developed models were verified and validated using such experiments as uniaxial compression/tension and indentation. The results of model tests showed that the developed elastic-plastic models of the implant material can be successfully used in further modelling the mechanical behaviour of the lumbar segment of the spine with the M6-L endoprostheses. [ABSTRACT FROM AUTHOR]

Modern technologies for the production of structural and functional materials make it possible to obtain highly efficient composites with a complex multilevel structure at various spatial scales. At present, methods for obtaining and studying the properties of dual composites, in which different compositions form a matrix and granules, have begun to be developed. In this work, we studied numerically the influence of the volume content of the TaB2-SiC granule in the ZrB2-SiC matrix on the effective hardness of such a dual composite using simulation of nanoindentation. The method of movable cellular automata was used as a simulation method. The results obtained showed that an increase in the volume content of TaB2-SiC granules from 10 to 30 % leads to an increase in hardness determined by indentation into the region between granules up to 15 % compared with a homogeneous distribution of TaB2 particles in the ZrB2(80)-SiC(20) composite (matrix of the dual composite). However, a further increase in the volume content of granules to 40–50 % leads to a decrease in the effective hardness of the dual composite. [ABSTRACT FROM AUTHOR]

Arthritis is a degenerative disease of the musculoskeletal system that has the most destructive effect on cartilage. Physiotherapy is used to improve the condition of biological tissues. One of the methods of outer mechanical action, which has a therapeutic effect, is ultrasonic wave (USW) loading. In this work, on the basis of computer simulation, a study was made of the effect of different USW intensities on the repair of tissues of cartilage layer and meniscus in the knee joint. It was found that the circumstances for the repair of biological tissues of the knee joint are created with USW with an intensity of more than 1 W/cm2. [ABSTRACT FROM AUTHOR]

Arthritis is a dangerous degenerative disease of the knee joint, affecting primarily cartilage and meniscus. External acoustic stimulation is nowadays increasingly used to treat arthritis. This article presents the first model of the knee joint, based on the approach of computational particle mechanics and intended for a virtual study of the parameters of external mechanical impact on its therapeutic effectiveness. The constructed model was thoroughly verified and validated. The analysis of the conditions for the regeneration of the tissues of the knee joint under ultrasound exposure was carried out. The results obtained indicate the possibility of achieving the required level of the stresses and strains under loading with intensity higher than 1 W/cm2. [ABSTRACT FROM AUTHOR]

In this paper, the effective mechanical characteristics of porous ceramics were determined using numerical modeling of tension and compression of a representative volume in the 2D statement. An approach for numerical determination of the effective characteristics is described. The specific features of the proposed approach are the use of the real microscopic structure of porous ceramics without conducting fracture tests and the possibility to determine various elastic moduli carrying out only a single calculation. Thus, this approach allows for determining the effective mechanical properties of porous ceramics by having only their microscopic structure and the properties of corresponding non-porous material. The obtained effective elastic moduli and strength characteristics of porous corundum ceramics show good agreement with the experimental data obtained. [ABSTRACT FROM AUTHOR]

Nanostructuring burnishing is a promising kind of finishing and hardening surface processing. To provide nanostructure formation in the burnished surface layers, special stress conditions have to be realized, which are controlled by the parameters and regimes of the processing. Additional research support is needed in the case of varying burnishing tools and materials. The paper investigates the influence of parameters concerning a new type of the burnishing tool shape on the distributions of stress, temperature, and plastic strain in the steel surface layer during the treatment. The investigation was conducted by finite element analysis using Abaqus/Explicit computer code. [ABSTRACT FROM AUTHOR]

External shock-wave loading is used in therapeutic dosages for the prevention and treatment of fractures. Features of a patient's physiological condition (age, illness, injury) require an individual choice of the parameters of low-energy acoustic (mechanical) action. This paper presents the results of modeling an external shock-wave loading of varying intensity in the areas of the femoral, knee, and ankle joints of real geometry. The simulation results showed that the range of permissible loads that do not lead to degradation of bone tissue, depending on the geometry of the bone, should be selected with taking into account the area of acoustic exposure. The safest is low-intensity exposure. [ABSTRACT FROM AUTHOR]

Computer simulation is an important stage in the development of new materials. The aim of this work is to identify the conditions for the realization of the effect of structural adaptability in the composites based on aluminum bronze with inclusions of boron carbide in sliding friction based on 3D computer simulation. The method of movable cellular automata, which is an original implementation of the concept of discrete elements, was used for numerical modeling. We simulated three-dimensional samples at the scale of single roughness asperities studied previously in the two-dimensional approximation. It was shown that a mixing zone with a width of about two micrometers is formed between the interacting bodies, where the "micro-wedge" region can be identified. Rotating wear particles typical for 2D calculations in the plane-stressed state were not observed. Thus, the results of three-dimensional calculations are more consistent with the plane strain approximation. The introduction of strengthening particles of boron carbide into the contact area with a local concentration of 5 and 10 volume percent does not strongly affect the value of the friction coefficient, but leads to its stabilization. The analysis of equivalent stress fields shows, that a decrease in the size of the "wedges" leads to a decrease in the stresses concentration in the region of their interaction with the base material of the sample. Thus, the results of three-dimensional simulations obtained correspond to the data of two-dimensional calculations and the experimental regularities of the mechanical and tribological tests of gradient materials based on aluminum bronze with boron carbide inclusions manufactured by the method of electron beam additive deposition. [ABSTRACT FROM AUTHOR]

The method of movable cellular automata (MCA) has been successfully used to simulate the mechanical behavior of materials under severe deformation conditions for over 20 years. One of the important applications of the MCA method is friction. In most of the published results obtained within the MCA method, the region where actually friction of metallic materials occurs consists of a so-called quasi-liquid layer, i.e., a mixing zone of particles detached from the base material and forming a dynamic system, where inter-particle bonds are constantly switching between two basic states: bonded and unbonded. In this work, we try to reveal the influence of the criteria of breaking and the formation of bonds between elements of the MCA method on the features of the structure formation in the friction layer for metallic materials. For this purpose, a new fracture criterion was implemented, based on the specific work of elastic-plastic deformation in the interaction point of movable cellular automata. Test calculations have shown that the use of such a criterion makes it possible to significantly expand the capabilities of the method for describing structure formation in the friction zone of metallic materials. [ABSTRACT FROM AUTHOR]

The samples of the promising Cu-Al-Ni alloys were fabricated by electron-beam additive printing and studied by electron microscopy. The fabrication was carried out using the combined powder feed and wire feed technology. The samples obtained by specific selecting the printing regime, varying the degree and mode of post-processing, were characterized by homogeneous chemical composition structure. The microstructure and elements distribution of the obtained material was determined by scanning electron microscopy. In the case of printing without additional electron-beam treatment, an irregularity of the microstructure, chemical composition, precipitation of intermetallic phases was observed. [ABSTRACT FROM AUTHOR]

Degenerative diseases and injuries of the spine are one of the main reasons for the disability of the population. Total discs arthroplasty is the main treatment for severe spinal diseases. Hence, an overview of the methods used for studying the mechanical behavior of spinal tissues during endoprosthesis replacement becomes topical. Herewith we describe the methods of an experimental and numerical study of the mechanical characteristics and functional properties of tissue and the spine elements that endoprosthesis must meet. The need is shown to develop methods for the numerical study of the mechanical behavior of the lumbar vertebrae during arthroplasty, taking into account degenerative changes in biological tissues. [ABSTRACT FROM AUTHOR]

Diseases of the musculoskeletal system significantly reduce the quality of human life. For the treatment of degenerative changes of mild to moderate severity are used non-pharmacological methods based on mechanobiological principles. Shock wave therapy is one of the methods of external mechanical stimulation of biological tissue regeneration. In this work was created a numerical model of the knee joint to study its mechanical behavior under acoustic exposure. The simulation results show that at low intensity shock-wave action allows obtaining the conditions required for tissue regeneration mainly in the surface layers of the constituent elements of the knee joint. [ABSTRACT FROM AUTHOR]

Degenerative diseases of the spine tissues significantly reduce the human capability for an active life. Intervertebral discs are subject to the greatest degradation among other spinal parts. It is promising to use computer simulation for estimating the stress state and then revealing the factors affecting possible damages of the disc. Intervertebral disc is a sophisticated spinal element consisting of several materials (the nucleus, the annulus, and the cartilaginous endplates). Therefore, to develop a numerical model of the intervertebral disc, it is necessary to verify and validate the models of the materials. This paper presents new numerical models of the materials of the intervertebral disc; validation and verification of the models are performed. Validation of the models was carried out using numerical tests on tension, compression, and indentation. Good qualitative and quantitative compliance with the data of real experiments was obtained. [ABSTRACT FROM AUTHOR]

The creation of functional materials is a promising direction for engineering development. Functional materials include metamaterials among others. Metamaterials achieve the required properties using a rationally designed structure. Tetrachiral structures differ from the others in that they can twist under uniaxial loading. This paper solves the quasi-static problem of uniaxial loading within the framework of linear elasticity theory using the finite element method. It is investigated how the support reaction changes when a second ring is added into the chiral structure. The dependence obtained suggests that by adding a complementary ring and increasing its size more forces have to be applied to deform the metamaterial. It is shown how the size of the secondary ring affects Young's modulus. [ABSTRACT FROM AUTHOR]

In the paper using the molecular dynamics method, several combinations of interatomic potentials are analyzed to describe the interaction of elements of a multicomponent Al-Cu-Ni alloy. The possibility of describing martensitic transformations proceeding under conditions of thermomechanical action was investigated. The studies made it possible to construct a physically correct model of the Al-Cu-Ni alloy and to analyze some regularities of structural transformations occurring in it under mechanical action and heating. The constructed model can be used for further research using a numerical experiment. [ABSTRACT FROM AUTHOR]

Ceramic composites based on a ZrB2 matrix with inclusions of SiC and MoSi2 particles are considered. The volume fraction of both types of inclusions, their size, and their location in space varied. To study the effect of the structure of composites on their compressive strength, a computer model of the unit cell of the corresponding composites was developed using the method of movable cellular automata. As a result of computer simulation, the features of the mechanical behavior of the composites ZrB2-X(SiC)-Y(MoSi2) with different designs of the structural-phase hierarchy were revealed. It is shown that ceramics with a dual composite structure, where inclusions of MoSi2 form mesoscopic granules, have better mechanical characteristics due to the inhibition of microcrack propagation compared to a material with a uniform arrangement of both types of inclusions in the bulk of the composite. [ABSTRACT FROM AUTHOR]

Degenerative diseases, injuries of the musculoskeletal system significantly reduce the quality of human life. Shock-wave loading is used to treat degraded bone tissue. This paper presents the results of numerical simulation of shock-wave loading of two-layer model samples of healthy biological tissues and those affected by osteoarthritis and osteoporotic arthritis. It was found that low-intensity acoustic exposure of the cortical tissue creates conditions for the treatment of osteoporotic phenomena. The application of a load in the area of cartilage promotes the generation of bone and biological tissues at great depths from the loading source. [ABSTRACT FROM AUTHOR]

To enhance the functional properties of aluminum bronze, different reinforcing inclusions may be used to produce metal matrix composite. In this study, we proposed a numerical model to investigate the influence of different spatial distributions of boron carbide particles in the bronze matrix on such mechanical properties as tensile strength and hardness. The model is based on the method of movable cellular automata, which is a representative of computational particle mechanics and allows considering the composite structure explicitly. The simulation results show that introducing boron carbide inclusions into aluminum bronze matrix leads to enhancing the hardness and tensile strength but reducing the ultimate strain in tension. The gradient distribution of the inclusion fraction with the maximum value on the surface allows getting higher hardness than the uniform distribution. The size of the reinforcing particles has no great influence, while the volume fraction and type of spatial distribution are of great importance for the mechanical properties considered in this study. It is also shown that boron carbide inclusions serve as a source of crack initiation under mechanical loading. [ABSTRACT FROM AUTHOR]

This work is devoted to the refinement of the previously developed numerical models of the frictional contact of composites based on iron oxide. The most important point is taking into account the plastic properties of iron oxide, which were determined from the experimental data on its constrained compression from the literature. To adjust them, we simulated the penetration of a Vickers indenter into an iron oxide specimen and compared the obtained load-displacement curve with the experimental data from other experiments. The second refinement of the proposed model consists of using the full three-dimensional geometry instead of the plane stress approximation. Periodic boundary conditions are still used in the sliding direction; however, the three-dimensionality of the problem makes it possible to more accurately take into account the size of inclusions and the formed dynamic inhomogeneities in the friction layer. The third refinement of the model is taking into account the heat release during friction due to plastic deformation, as well as the effects of thermal expansion and thermal conductivity. [ABSTRACT FROM AUTHOR]

We model the mechanical behavior of tibia as a 3D poroelastic composite consisting of the interior cancellous part and the outer cortical part. For simplicity, both parts are assumed to be isotopic linear poroelastic material but possessing different values of porosity, fluid content and elastic properties, which are taken from literature. For computer simulation, we used the movable cellular automaton method, which is a representative of simply deformed discrete elements. The method allows simulating dynamics of the elastic skeleton deformation and viscous fluid flow in the skeleton pores according to Biot's theory of linear poroelasticity. Using the model developed we study the mechanical behavior of tibia in dynamic compression with different rate of loading and different boundary conditions. The results obtained for both saturated and drained bones are discussed in terms of getting a better model. [ABSTRACT FROM AUTHOR]

Ultrasound therapy looks very promising to treat degenerative changes in the musculoskeletal system and fractures. Computer simulation can help to reveal the acoustic low-energy effects on bone tissue. Usually, the model samples with averaged mechanical characteristics are used to simplify the simulations. However, such assumptions can distort the resulting stress and strain fields, which in turn could lead to an incorrect prediction of the bone tissue regeneration. This paper presents the results of ultrasound exposure of model samples of an elementary form of various compositions with explicit and implicit consideration of the biological tissue structure. The results obtained indicate a gradient distribution of the stress/strain fields with a decrease in the amplitude of the output parameters for model samples with averaged mechanical properties and a two-component composition (cortical and spongy tissue). The interface between the tissues serves as a "secondary" acoustic source as well as a barrier in the case of a two-component "cartilage-cortical tissue" model specimen; the maximum stresses are concentrated there. [ABSTRACT FROM AUTHOR]

The paper deals with the problem of deforming a mechanical metamaterial. The metamaterial is constructed from chiral elements comprising rings and ribs. The behavior of the bulk metamaterial sample during compression was studied numerically in the framework of linear elasticity theory. Due to the chiral structure, the metamaterial sample exhibits unusual effects. One of them relates to nonlinear transformations, namely a twist. It was found that the deformations are distributed irregularly over the material. During the compression of the metamaterial sample, the rings undergo a torque, and the ribs begin to bend. All the ribs of the metamaterial sample undergo similar bending. Additionally, there are areas affected by two codirectional bends with different signs. Strain localization and the corresponding stress concentrations are of great importance from the strength analysis point of view. As for Young's modulus, it is significantly (by 100 times) less for the metamaterial sample than for the base material. It is justifiable since the ratio of the volume of a base solid to the volume of the metamaterial is quite large. When constructed the tetrachiral structure, the porosity value is 98%. [ABSTRACT FROM AUTHOR]

The paper deals with a 2D metamaterial constructed from chiral elements comprising rings and ligaments (ribs). The behavior of the metamaterial during tension was studied by numerical modeling. The shear deformation appears within the tetrachiral honeycomb under uniaxial loading. It is found that coupling exists between the elongation and inclination of the sample with tetrachiral honeycomb structure and this causes some ambiguity when calculating the effective Poisson's ratio. The coupling effect depends on both the honeycomb's deformation and the geometric parameters of the cell structure. This special coupling effect of tetrachiral honeycombs provides a new idea for designing new metamaterials. An analytical expression for this effective Poisson's ratio is derived. In the process of uniaxial loading, the reason for the elongation of the specimen was found. [ABSTRACT FROM AUTHOR]

In this paper, the states of stress and strain in the deep structures in the Yakutsk-Vilyui large igneous province (LIP) are numerically analyzed. The "Craton-1980" profile with 60 km depth was chosen because it is characteristic for the Yakutsk-Vilyui LIP and contains deformed crystalline foundation and the upper mantle layer. This geological profile was obtained by deep seismic sounding surveys. Using the "Craton-1980" profile data a 2D computer structural model was constructed. To solve the posed problem, a model of the continental yield stress envelopes (YSE) was used in which the strength properties of Earth's crust layers change in accordance with depth and due to the influence of heat flow from the mantle layer. To describe the inelastic properties, the use of Nikolaevskiy's elastoplastic model was made. Numerical simulation allowed for revealing the regions in the lithosphere responsible for the formation of stress concentrations and inelastic strain localization. The location of these regions was shown to be determined not only by the heterogeneous layers in Earth's crust with curved interfaces but also by pronounced non-monotonic dependence of strength with depth. [ABSTRACT FROM AUTHOR]

We studied the possibility to produce a high-performance metal matrix composite (MMC) based on aluminum bronze with reinforcing particles of boron carbide. MMC was manufactured by electron beam additive printing method using CuAl bronze wire and B4C powder. The hardness and structure of the produced material were studied. It was found that a strong gradient of the powder along the height of the MMC was formed in the printed material. The formation of this gradient results in an uneven increase in hardness in the composite layer of the sample. [ABSTRACT FROM AUTHOR]

Degenerative diseases and injuries of the musculoskeletal system and bone fractures, significantly affect the quality of human life. External low-energy impact can be used for their treatment. Recently, computer simulation has been applied to study the possibilities of using ultrasonic loading and selecting the optimal loading parameters that contribute to the bone tissue regeneration. This paper presents the results of verification and validation of the proposed bone tissue models under dynamic impact. The results of an analysis of the sensitivity of bone tissue models to strain rates are also discussed. The data obtained indicate that in the case of using an elastic model of the medium for bone tissue, the dependence of the strength properties on the loading rate has a monotonic linear character. In the case of poroelastic models, such a dependence has a sigmoid nonlinear character. [ABSTRACT FROM AUTHOR]

In the framework of the asymmetric theory of the elastic-plastic Cosserat continuum in a two-dimensional formulation for plane strain, the simulation of inelastic localized deformation was performed for homogeneous samples and the mesoscale volumes of the polycrystalline material. It is assumed that the development of rotational deformation modes in loaded materials is associated with the development of localized plastic deformation in them and the formation of curvatures of the crystal lattice in the material at the micro and nanoscales. For this reason, the parameters of the Cosserat model are considered as functions of inelastic strain for each local volume of the medium. It is shown that the couple stress forming at the mesoscale makes a significant contribution to the hardening of macroscopic stress-strain curves. The simulation results show that if the rotation modes of deformation are blocked in the loaded material, the accommodation capacity of the material decreases, the local and macroscopic degree of inelastic strain sharply increases and fracture patterns are formed much faster. Conversely, the creation of meso- and nanosized substructures with a high curvature of the crystal lattice in materials contributes to the activation of rotational deformation modes, reducing the degree of localized strain and relaxation of dangerous stress concentrators. [ABSTRACT FROM AUTHOR]

The physical and mechanical properties of heterogeneous materials are mainly determined by their structure. Due to the wide capabilities of modern technologies for the formation of complex multilevel pore structure of ceramics and other materials, the ability of modern methods to describe and characterize such a structure completely is of particular interest. Traditionally, the structure of the pore space is characterized by a large number of parameters such as porosity, type and shape of pores, the fraction of cross-sectional area of channels, pore size distribution, etc. However, recently, at least three new quantities are often used to describe and measure the structure of various complex media: the Minkowski functionals, fabric tensors, and correlation functions. This review is aimed to consider all these three approaches and their capabilities for describing and measuring the peculiarities of the structure of porous materials. [ABSTRACT FROM AUTHOR]

The paper reports the numerical results of modeling slow deformation autowaves in solids. To perform the simulation, we used solid mechanics approach with J2 plasticity combined with N-shaped softening-hardening law. The results show that at first plastic strain originates at the stress concentrators and propagates across the specimen with rather high speed about 1 km/s. Thereupon, the region of plastic strain expands due to fronts propagating at speed about 2–6 m/s that is several times greater than the loading velocity. The motion of such kind of deformation autowaves is not steady, so the speeds mentioned above are averaged values. The shapes of original plastic strain zones and propagating fronts vary with changing the governing parameters of N-shaped local stress-strain curve. Variation of these parameters in the given ranges affects the speed of propagating deformation autowave only slightly. [ABSTRACT FROM AUTHOR]

The possibilities of numerical modeling to determine the impact of discharge wells on the change in the stress-strain state and damage in the coal seam and the surrounding rock mass near the mine workings are shown. Numerical modeling is carried out on the base of the evolutionary approach being developed by the authors and using the finite difference method. The results indicating the unloading of the drilled regions of the coal seam were obtained. The fracture patterns of coal near wells are obtained and studied. Local and averaged characteristics of stress, inelastic strain and damage are analyzed. [ABSTRACT FROM AUTHOR]

There are many methods for direct assessment of the mechanical properties of bone tissue, such as tension, compression, and three-point bending tests. However, all these methods are used for testing the bone extracted from the body and usually specially treated, and therefore do not provide the characteristics necessary for clinical practice. Recently, however, indentation has become positioned as a procedure for clinical use with minimal invasiveness. In addition, with the help of microindentation, a local study of the affected areas of bone tissue is possible. At present, non-invasive methods for diagnosing bone properties are being actively developed, based on visualization of the structure of bone tissue, followed by importing the information obtained into computer modeling software systems. This paper presents a numerical model of the mechanical behavior of cancellous bone tissue as a poroelastic body. To test the model, the influence of such factors as the presence of fluid, loading with holding, loading rate, as well as the effect of permeability on the mechanical response of the bone tissue when the hard tip being penetrated was investigated. [ABSTRACT FROM AUTHOR]

Wear in friction pairs of the endoprosthesis plays an important role in the mechanical behavior of the bone-endoprosthesis system. To increase the wear resistance of metallic materials used in friction pairs, reinforcing coatings are applied. Tribological and mechanical properties of the coatings depend on application regimes. This paper presents a numerical study on modeling the process of sliding friction of two contacting surfaces of the ceramic coatings, applied under different regimes. The results obtained indicate the promise of using coatings applied under different deposition conditions for different parts of the friction pair. [ABSTRACT FROM AUTHOR]

TiN coatings obtained by PVD technology are used, in particular, to harden friction surfaces of biocompatible implants, including hip joint endoprosthesis. When introduced into the body, the surface of the coating begins to interact with biological fluids, which leads to changes in its physical and mechanical properties. Investigating the properties of the coating material saturated with biological fluid in the body (in vivo) is impossible. The study of this material in vitro is also difficult since it exists only in the form of a coating. However, using computer simulation it is possible to study its mechanical properties under conditions as close to the conditions in a living organism as possible, including liquid saturation. In this paper, we simulated uniaxial compression of a cubic sample of TiN coating under various conditions of fluid content, loading rate, and microporosity parameters. The results obtained indicate the sigmoidal nature of the dependencies of the mechanical properties of the coating on the loading conditions and microporosity parameters. [ABSTRACT FROM AUTHOR]

The paper is devoted to the numerical study of the mechanical behavior of materials in the friction pair of healthy bone and hip resurfacing endoprosthesis. The investigation was based on three-dimensional computer simulation by the movable cellular automaton method, which is a representative of the particle based methods in mechanics of materials. It is shown that the use of coated titanium alloys in the friction pair of the hip joint endoprosthesis promotes long-term use of the endoprosthesis without frequent revision operations. However, the stress field in the friction pair of the endoprosthesis is quite different from one of the healthy hip joint, which in turn can affect the condition of the musculoskeletal system as a whole. [ABSTRACT FROM AUTHOR]

In this paper, the states of stress and strain in the deep structures in the Yenisei Ridge were numerically analyzed. The “Shpat” profile with 60 km depth was chosen because it is characteristic for the Yenisei Ridge due to its layer structure of Earth’s crust and the presence of deep lense. This geological profile was obtained by deep seismic sounding surveys. To solve the posed problem, two models of the continental yield stress envelopes (YSE) are used, where strength properties change in accordance with depth and due to the influence of heat flow from mantle layer. To describe the inelastic properties, Nikolaevskiy’s elastoplastic model is used. On the basis of presented models, it was educed that there are some regions both near the Earth surface and in the deep layers, which are responsible for the formation of stress concentrations and the subsequent strain localization in the form of thrusts, bands of localized shear, etc. Not only the heterogeneous layering of Earth’s crust with curved interfaces but also non-monotonic dependence of strength with depth determine the location of these regions. [ABSTRACT FROM AUTHOR]

This paper analyzes numerically the mechanical behavior of geological depth structures in the Yenisei Ridge. For creating the computer structures of the researched area, the two geological profiles of “Shpat” and “Batolit-1982” obtained by deep seismic sounding were taken as a basis. To model plastic deformation, the Nikolaevsky elasto-plastic model was used. The depth analysis of the state of stress and strain was realized making use of the inelastic strain increments and the Lode parameter. The maximum values of strain increments are focused in upper layers of Earth’s crust, where pressure is lower, and also in the region of the Yenisei shear belt. The view of the Lode parameter distribution closely depends on the variation of strength properties with depth in the lithosphere. The stress state of the geological profiles “Shpat” and “Batolit-1982” is very heterogeneous, that is caused not only by the difference of physical and mechanical properties of lithosphere layers but the change of the geomedia strength with depth as well. [ABSTRACT FROM AUTHOR]

The paper presents a multiscale model for porous ceramics based on movable cellular automaton method, which is a particle method in novel computational mechanics of solid. The initial scale of the proposed approach corresponds to the characteristic size of the smallest pores in the ceramics. At this scale, we model uniaxial compression of several representative samples with an explicit account of pores of the same size but with the unique position in space. As a result, we get the average values of Young's modulus and strength, as well as the parameters of the Weibull distribution of these properties at the current scale level. These data allow us to describe the material behavior at the next scale level were only the larger pores are considered explicitly, while the influence of small pores is included via effective properties determined earliar. If the pore size distribution function of the material has N maxima we need to perform computations for N-1 levels in order to get the properties step by step from the lowest scale up to the macroscale. The proposed approach was applied to modeling zirconia ceramics with bimodal pore size distribution. The obtained results show correct behavior of the model sample at the macroscale. [ABSTRACT FROM AUTHOR]

The paper presents a computational model for the numerical study of the mechanical behavior of ceramics with an explicit account of its internal structure, namely, cylindrical pores differently oriented in space. The model utilizes the movable cellular automaton method for modeling deformation and fracture as dynamic processes occurring in the material under loading. We model uniaxial compression of several representative 3D cubic specimens with an explicit account of pores of the same size but with a unique position and orientation in space. As a result, we get the average values of Young’s modulus, Poisson’s ratio, and strength, as well as the parameters of the Weibull distribution of these properties of the model material. The analysis of the modeling results shows that the minimum values of mechanical properties is exhibited by the specimens with all cylindrical pores inclined at the angle of 45° to the loading direction. The randomization of the elongated pore orientation leads to higher mechanical properties. [ABSTRACT FROM AUTHOR]

The hip joint is an important element of the human musculoskeletal system. Endoprosthetics is used to treat pathology of the hip joint. The wear in the friction pair of the composite elements of the endoprosthesis significantly reduces the operating life of the prosthesis. In this case, the structure of the surface layers of the contacting elements plays a key role in the wear process. To improve the mechanical and tribological characteristics of surface layers, hardening coatings are used. In this study, we use computer simulation of three-point bending for investigating the mechanical behavior of the coating-substrate system, which is created using different regimes of coating deposition. Based on the results of the modeling, it has been found that the best adhesion of the coating and the flexural strength is provided by the system coated with the use of the third mode. [ABSTRACT FROM AUTHOR]

In this paper the physical-mathematical model of the stress-strain state evolution of loaded rocks is developed with the purpose of numerical simulation of deformation up to failure of Cenozoic sedimentations typical for epicentral zone of Chuya earthquake. Sedimentations of Chuya and Kuray depressions are represented mostly by clays, pebbles and other loose rocks with different inclusions of calcium phosphate, feldspar, dolomite, quartz, etc. A combination of two models of inelastic behavior is used in this study, namely, an elliptic shaped yield surface for clays and the modified Drucker-Prager-Nikolaevskii model for different inclusions. The psammopelite structure of clay with debris of shark teeth (calcium phosphate) and decomposed feldspar is loaded up to failure. [ABSTRACT FROM AUTHOR]

In this paper, the mechanical behavior of marble mesovolumes is numerically analyzed by taking into account their structures. Experimental data characterizing porosity and grain structure are used to generate geometrical computer models. To model inelastic deformation, the Nikolaevskiy elastic-plastic model is used. The failure criterion, which combines plastic strain and tensile stress limits, is adopted for the description of mesovolume fracture. The problems are solved with the application of the numerical finite difference method. Mesovolumes with porosity prove to fail fast, due to pores, which are strong stress concentrators. Besides, pore-free mesovolumes withstand long-time loading without failure. Accumulation of inelastic strain and damage takes place in grains with low strength properties. These results may be necessary for mining, underground construction, and other applications. [ABSTRACT FROM AUTHOR]

The paper reports the simulation results of mechanical behavior of porous ceramics based on aluminum oxide. A mechanical response of porous ceramic materials is described using the mathematical model of an elastic-brittle-plastic medium and various fracture criteria. Depending on the chosen fracture criterion, the width of fracture zones and the averaged loading diagram form are shown to change. With the maximum inelastic strain fracture criterion, the loading diagram most closely corresponds to brittle material; with the accumulated damage criterion, it corresponds to ductile material. The fracture zones are maximum for the strain criterion and narrowest for the damage criterion. [ABSTRACT FROM AUTHOR]

The paper presents an experimental investigation of the mechanical behavior of specimens made of alumina ceramics prior to catastrophic fracture and the transition to the blow-up mode. Ceramic specimens are tested in three point bending and uniaxial compression tests. The surface velocity of the loaded specimens is registered using a laser Doppler vibrometer. The duration of the stage of a catastrophic increase in the lateral surface velocity prior to fracture is approximately half a millisecond in three-point bending tests and about 0.1 ms in compression tests. [ABSTRACT FROM AUTHOR]