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The interaction of water with confining surfaces is primarily governed by the wetting properties of the wall material—in particular, whether it is hydrophobic or hydrophilic. The hydrophobicity or hydrophilicity itself is determined primarily by the atomic structure and polarity of the surface groups. In the present work, we used molecular dynamics to study the structure and properties of nanoscale water layers confined between layered metal hydroxide surfaces with a brucite-like structure. The influence of the surface polarity of the confining material on the properties of nanoconfined water was studied in the pressure range of 0.1–10 GPa. This pressure range is relevant for many geodynamic phenomena, hydrocarbon recovery, contact spots of tribological systems, and heterogeneous materials under extreme mechanical loading. Two phase transitions were identified in water confined within 2 nm wide slit-shaped nanopores: (1) at p1 = 3.3–3.4 GPa, the liquid transforms to a solid phase with a hexagonal close-packed (HCP) crystal structure, and (2) at p2 = 6.7–7.1 GPa, a further transformation to face-centered cubic (FCC) crystals occurs. It was found that the behavior of the confined water radically changes when the partial charges (and, therefore, the surface polarity) are reduced. In this case, water transforms directly from the liquid phase to an FCC-like phase at 3.2–3.3 GPa. Numerical simulations enabled determination of the amount of hydrogen bonding and diffusivity of nanoconfined water, as well as the relationship between pressure and volumetric strain.

Computer modelling is a key tool in the optimisation and development of ceramic refractories utilised as insulation in high-temperature industrial furnaces and reactors. The paper is devoted to the mesoscale computer modelling of silica refractories using the method of homogeneously deformable discrete elements. Approaches to determine the local mechanical properties of the constituents from the global experimental failure parameters and respective crack trajectories are considered. Simulations of the uniaxial compressive and tensile failure in a wide range of quasi-static and dynamic loading rates (102 s−1) are performed. The upper limit of the dynamic loading rates corresponds to the most severe loading rates during the scrap loading on the refractory lining. The dependence of the strength, fracture energy, and brittleness at failure on the loading rate is analysed. The model illustrates that an increase in the loading rate is accompanied by a significant change in the mechanical response of the refractory, including a decrease in the brittleness at failure, a more dispersed failure process, and a higher fraction of the large grain failure. The variation of the grain–matrix interface’s strength has a higher impact on the static compressive than on the static tensile properties of the material, while the material’s dynamic tensile properties are more sensitive to the interface strength than the dynamic compressive properties.

It is well-known that the effect of interstitial fluid on the fracture pattern and strength of saturated high-strength concrete is determined by qualitatively different mechanisms at quasi-static and high strain rate loading. This paper shows that the intermediate range of strain rates (10−4 s−1 &lt, ε˙ &lt, 100 s−1) is also characterized by the presence of a peculiar mechanism of interstitial water effect on the concrete fracture and compressive strength. Using computer simulations, we have shown that such a mechanism is the competition of two oppositely directed processes: deformation of the pore space, which leads to an increase in pore pressure, and pore fluid flow. The balance of these processes can be effectively characterized by the Darcy number, which generalizes the notion of strain rate to fluid-saturated material. We have found that the dependence of the compressive strength of high-strength concrete on the Darcy number is a decreasing sigmoid function. The parameters of this function are determined by both low-scale (capillary) and large-scale (microscopic) pore subsystems in a concrete matrix. The capillary pore network determines the phenomenon of strain-rate sensitivity of fluid-saturated concrete and logistic form of the dependence of compressive strength on strain rate. Microporosity controls the actual boundary of the quasi-static loading regime for fluid-saturated samples and determines localized fracture patterns. The results of the study are relevant to the design of special-purpose concretes, as well as the assessment of the limits of safe impacts on concrete structural elements.

The paper describes an advanced discrete-element based mechanical model, which allows modelling contact interaction of ductile materials with taking into account fracture and surface adhesion by the cold welding mechanism. The model describes these competitive processes from a unified standpoint and uses plastic work of deformation as a criterion of both local fracture and chemical bonding of surfaces in contact spots. Using this model, we carried out a preliminary study of the formation of wear particles and wedges during the friction of rough metal surfaces and the influence of the type of forming third body (interfacial) elements on the dynamics of the friction coefficient. The qualitative difference of friction dynamics in the areas of the contact zone characterized by different degrees of mechanical confinement is shown.

The chapter presents recent advances in developing numerical models for multiscale simulation of the femur–endoprosthesis system for the case of hip resurfacing arthroplasty. The models are based on the movable cellular automaton method, which is a representative of the discrete element approach in solid mechanics and allows correctly simulating mechanical behavior of a variety of elastoplastic materials including fracture and mass mixing. At the lowest scale, the model describes sliding friction between two rough surfaces of TiN coatings, which correspond to different parts of the friction pair of hip resurfacing endoprosthesis. At this scale, such parameters of the contacting surfaces as the thickness, roughness, and mechanical properties are considered explicitly. The next scale of the model corresponds to a resurfacing cap for the femur head rotating in the artificial acetabulum insert. Here, sliding friction is explicitly computed based on the effective coefficient of friction obtained at the previous scale. At the macroscale, the proximal part of the femur with a resurfacing cap is simulated at different loads. The bone is considered as a composite consisting of outer cortical and inner cancellous tissues, which are simulated within two approaches: the first implies their linear elastic behavior, the second considers these tissues as Boit’s poroelastic bodies. The later allows revealing the role of the interstitial biological fluid in the mechanical behavior of the bone. Based on the analysis of the obtained results, the plan for future works is proposed.

The authors outline the results of long-term interdisciplinary research aimed at identifying the possibility and the methods of controlling tangential displacements in seismically dangerous faults to reduce the seismic risk of potential earthquakes. The studies include full-scale physical and numerical modeling of P-T conditions in the earth’s crust contributing to the initiation of displacement in the stick-slip regime and associated seismic radiation. A cooperation of specialists in physical mesomechanics, seismogeology, geomechanics, and tribology made it possible to combine and generalize data on the mechanisms for the formation of the sources of dangerous earthquakes in the highly stressed segments of faults. We consider the prospect of man-caused actions on the deep horizons of fault zones using powerful shocks or vibrations in combination with injecting aqueous solutions through deep wells to manage the slip mode. We show that such actions contribute to a decrease in the coseismic slip velocity in the fault zone, and, therefore, cause a decrease in the amplitude and energy of seismic vibrations. In conclusion, we substantiate the efficiency of the use of combined impacts on potentially seismically hazardous segments of fault zones identified in the medium-term seismic prognosis. Finally, we discuss the importance of the full-scale validation of the proposed approach to managing the displacement regime in highly-stressed segments of fault zones. Validation should be based on large-scale tests involving advanced technologies for drilling deep multidirectional wells, injection of complex fluids, and localized vibrational or pulse impacts on deep horizons.

Methods of particles are now recognized as an effective tool for numerical modeling of dynamic mechanical and coupled processes in solids and liquids. This chapter is devoted to a brief review of recent advances in the development of the popular particle-based discrete element method (DEM). DEM is conventionally considered as a highly specialized technique for modeling the flow of granular media and the fracture of brittle materials at micro- and mesoscopic scales. However, in the last decade, great progress has been made in the development of the formalism of this method. It is largely associated with the works of the scientific group of Professor S. G. Psakhie. The most important achievement of this group is a generalized formulation of the method of homogeneously deformable discrete elements. In the chapter, we describe keystones of this implementation of DEM and a universal approach that allows one to apply various rheological models of materials (including coupled models of porous fluid-saturated solids) to a discrete element. The new formalism makes possible qualitative expansion of the scope of application of the particle-based discrete element technique to materials with various rheological properties and to the range of considered scales form microscopic to macroscopic. The capabilities of this method are especially in demand in the study of the features of contact interaction of materials. To demonstrate these capabilities, we briefly review two recent applications concerning (a) the effect of adhesive interaction on the regime of wear of surface asperities under tangential contact of bodies and (b) the nonmonotonic dependence of the stress concentration in the neck of the human femur on the dynamics of hip joint contact loading.

This introductory chapter is dedicated to the life and work of Sergey Grigirievich Psakhie, his outstanding contributions to the development of science and education in Russia and especially in the Tomsk region as well as to his numerous international collaborations and research interests. It further includes personal notes from some of his closest collaborators: Georg-Peter Ostermeyer, Valentin L. Popov, Lev B. Zuev and Valery V. Ruzich. The Chapter is concluded by an overview of Sergey G. Psakhie’s most significant scientific publications.

Recent studies have shown that the use of membranes based on artificial nanoporous materials can be effective for desalination and decontamination of water, separation of ions and gases as well as for solutions to other related problems. Before the expensive stages of synthesis and experimental testing, the search of the optimal dimensions and geometry of nanopores for the water desalination membranes can be done using computer-aided design. In the present study, we propose and examine the assumption that rectangular nanopores with a high aspect ratio would demonstrate excellent properties in terms of water permeation rate and ion rejection. Using the non-equilibrium molecular dynamic simulations, the properties of promising hexagonal boron nitride (h-BN) membranes with rectangular nanopores were predicted. It has been found that not only the nanopore width but also its design (&ldquo, armchair&rdquo, or &ldquo, zigzag&rdquo, ) determines the permeability and ion selectivity of the h-BN-based membrane. The results show that membranes with a zigzag-like design of nanopores of ~6.5 &Aring, width and the armchair-like nanopores of ~7.5 &Aring, width possess better efficiency compared with other considered geometries. Moreover, the estimated efficiency of these membranes is higher than that of any commercial membranes and many other previously studied single-layer model membranes with other designs of the nanopores.

Surface temperature is among crucial factors which control wear during sliding dry contact. Using computer modeling, we study the possibility to achieve close to zero rate of surface wear during sliding friction of the special type of materials which possess negative thermal expansion. The numerical simulations reveal two wear regimes for materials with negative thermal expansion coefficient as dependent on the applied normal stress level. When the applied stress is lower than that of a critical level, a steady almost zero wear rate and nanorough surface are achieved during friction. Otherwise, wear rate is of the same order of magnitude as for "traditional" materials with positive thermal expansion coefficient. The critical stress value is analyzed depending on the material's mechanical, thermophysical, and surface roughness characteristics.

The paper presents an approach to developing the mathematical formalism of the discrete element method to numerically study the inelastic behavior and fracture of brittle materials under dynamic loading. The approach adopts the basic principles of the kinetic theory of strength which postulate the finite time of nucleation of discontinuities and relaxation of local stresses in the material. A general methodology is proposed for constructing dynamic (kinetic) models of the mechanical behavior of a discrete element based on quasi-static models and using three dynamic material parameters (time parameters). The physical meaning of these parameters is discussed, and a method is proposed for estimating the magnitude of the parameters for a considered material using standard experimental data on its mechanical characteristics. The approach is verified by a dynamic formulation of two-parameter models of inelasticity and strength of brittle materials within the method of simply deformable discrete elements. The proposed way to the dynamic generalization of conventional quasi-static mechanical models is applicable to various Lagrangian numerical methods and makes it possible to numerically study the dynamic behavior features and to predict the mechanical characteristics of brittle materials at different strain rates (up to strain rates 103 s−1) and different types of stress state.

In this paper, movable cellular automaton method (MCA) is applied to the multiscale simulation of 3D samples of ceramics composite with soft matter filler. MCA is an efficient numerical method in particle mechanics, which assumes many-particle interaction among discrete elements and makes a feasible simulation of solid behavior including deformation, crack initiation and propagation, and further fragmentation of the material at different scales. The lowest scale of the proposed model corresponds to the characteristic size of the smallest pores/inclusions. Herein we start with modeling uniaxial compression of several representative ceramics samples with an explicit account of small pores randomly distributed in space. The results are the average values of Young’s modulus, Poisson’s ratio, and strength, as well as the parameters of the Weibull distribution of these properties at the current scale. The data obtained allow us to describe the material behavior at the next scale were large cylindrical inclusions are considered explicitly, while the influence of small pores is accounted via the effective properties determined at the previous scale. The simulation results show that for each value of volume fraction of cylindrical soft inclusions there is no scattering of elastic modulus values while the scatter of strength and Poisson’s ratio values is significant. Random orientation of soft elongated inclusions results in higher strength value and does not change Young’s modulus of the model composites.

The paper is devoted to the numerical study of the dependence of uniaxial compressive strength of permeable fluid-saturated brittle solids on the loading rate. We analyzed the influence of strain rate, sample size, permeability of the material, fluid viscosity and a coefficient of the influence of pore pressure on the stress state of solid skeleton. We have shown that dynamic values of elastic modulus and strength of the sample is a unique nonlinear sigmoid-like function of the dimensionless parameter that characterizes the ratio of applied strain rate to interstitial fluid flow rate. We proposed the unified approximating function, which describes numerically derived dependences with good accuracy. The results of the study are relevant for estimating and forecasting dynamic compressive strength of the samples of different fluid-saturated brittle solids. Moreover, the proposed expression can be applied to determine unknown values of the fluid effect constants on the basis of reducing the experimental data to a unified curve.

The paper is devoted to the discussion of promising methods of man-caused impacts on highly stressed and potentially seismically dangerous segments of faults using the injection of drilling fluids through deep wells. We expect that fluid injection will make it possible to transfer displacements in the principal slip zone into the accelerated creep mode and thereby to exclude dynamic coseismic slip accompanied by high-amplitude elastic (seismic) waves. To substantiate the approach, we briefly analyze the information obtained from field experiments as well as physical and numerical modeling aimed to study the modes of generation of seismic impulses during dynamic slip events in fault segments. We also discuss the potential consequences of fluid injection into fault segments through deep wells.

In the paper, we developed a macroscopic discrete element model of permeable fluid-saturated materials with solid skeleton characterized by viscoelastic rheological properties. The Biot’s linear model of poroelasticity was used as a mathematical basis for describing the mechanical interrelation between the solid skeleton and interstitial fluid. Using this model, we numerically studied the dependences of the effective Young’s modulus and strength of fluid-saturated viscoelastic materials on the loading rate, sample size and the mechanical parameters, which determine the relaxation time of the solid-phase skeleton and the time scale of redistribution of fluid in the pore space. We revealed two dimensionless control parameters that determine the dynamic values of the effective mechanical characteristics of the samples under compression loading. We obtained the general relations that describe the above-mentioned dependences in terms of the two proposed control parameters. These relations have a logistic nature and are described by sigmoid functions. The importance of the proposed empirical expressions is determined by the possibility of their application for predicting the mechanical response of fluid-saturated materials of different nature (bone tissue, rocks, porous materials with polymeric skeleton, including elastomers, etc.) under dynamic loading.

In the paper, we developed a discrete element model of adhesive interaction of materials with taking into account the “cold welding” effect. Based on this model, we carried out a detailed analysis of the factors controlling regimes of adhesive wear for elastic-plastic materials with non-ideal plasticity. We proposed an empirical criterion of transition from “breakaway” to “grinding” regime of wear. The extended form of the given criterion takes into account the dependence of material strength on hydrostatic pressure.

A promising composite material for tribotechnical applications based on aluminum bronze with reinforcing boron carbide particles fabricated by a special electron beam additive deposition technique was studied experimentally and numerically. Tribological experiments showed that reinforcing by carbide particles allowed reducing the coefficient of friction from 0.26 to 0.19 and improving the wear resistance by 2.2 times. Computer modeling reveals two main factors playing a significant role in the friction behavior of the studied metal matrix composite: the mechanical effect of reinforcing ceramic inclusions and effective hardening of the metal matrix due to the peculiarities of the 3D electron beam printing. The mechanical effect of hardening inclusions determines a more rounded shape of wear particles, preventing wedging, and thereby increasing the stability of friction. Strengthening the metal matrix leads to reducing the number of wear particles.

The paper is devoted to a numerical analysis of the macroscopic mechanical characteristics of samples manufactured by electron-beam additive technology (3D printing) with metal wire. The results of computer simulation showed a pronounced anisotropy of the inelastic behavior of 3D printed samples and the dependence of their mechanical properties on the direction of wire deposition and on the width and mechanical characteristics of the layer interface zones. We empirically derived relations that make it possible to estimate the necessary parameters of interlayer interfaces (including yield stress and strain hardening modulus) to achieve the required mechanical characteristics of the product.

Based on the hybrid numerical method, namely, the hybrid method of movable cellular automata, we developed a computer-based two-scale mechanical model of heavy water-saturated concrete. The model takes into account the content of the liquid phase and its redistribution in networks of microscopic and capillary pores. The features of deformation and fracture of concrete samples under uniaxial compression were numerically studied in a wide range of variation of the macroscopic characteristics of the pore space, viscosity of an interstitial liquid and loading rate. Simulation results confirmed the possibility of a unified description of the dependence of the strength of heavy concrete on the sample permeability and size, fluid viscosity and the loading rate in terms of the complex dimensionless parameter that combines these characteristics.

The paper is devoted to the development of the formalism of the computational method of discrete elements (DEM) for describing the mechanical behavior of consolidated viscoelastic materials. We considered an advanced implementation of DEM, namely, the method of movable cellular automata (MCA). A feature of this implementation of DEM is the use of a generalized many-body formulation of the relations for the forces of element-element interaction. 3D numerical models of viscoelastic material with a spectrum of relaxation times (Kelvin and Maxwell models, the standard model of elastomers, and others) were developed within the formalism of MCA. The correctness of the developed discrete element formalism and its applicability for modeling the processes of deformation and fracture of viscoelastic materials under dynamic loading are shown using the standard model of elastomers as an example. The relevance of the results is determined by the prospects for the further development of DEM and its application to study and predict the mechanical response of viscoelastic materials of various nature under dynamic loading including contact problems.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in AIP Conference Proceedings 2167, 020075 (2019) and may be found at https://doi.org/10.1063/1.5131942. The paper reviews tangential adhesive contact of single asperities of elastic-plastic body surfaces. With the help of discrete element method we carried out a parametric study of influence of the parameters of adhesive interaction of the surfaces on the regime of asperity wear. It was established that with the adhesion work increase, the wear regime evolves from the mutual slippage of asperities to their attrition or brittle fracture, therewith the regime change has threshold nature. We obtained an empirical sigmoidal dependence of the threshold value of adhesion strength separating the slippage and attrition regimes on the strain-hardening coefficient of the material The results of the research make an important contribution to understanding the mechanisms that determine the development and intensity of wear in dry contact with adhesion.

In the paper, we theoretically studied the dynamics of mode II crack propagation in brittle solids with taking into account the finite duration of incubation of local fracture. The study was carried out by computer simulation using the movable cellular automaton method. We analyzed the influence of the magnitude of fracture incubation time on the fulfillment of the scale-invariance condition of dynamic crack propagation. We proposed a definition of this condition in terms of fracture incubation time and introduced a new physically based criterion to classify structural levels of fracture in brittle materials.

The experimental and theoretical studies on the search for the new promising filter materials and nanomaterials with superior permeability and specified selectivity of filtration intensively go ahead in the last decade. Theoretical studies are mainly based on molecular dynamics simulations of filtration and sieving of the fluids, gases and ions through the nanoporous materials of different nature. Layered or quasi-two-dimensional nanomaterials seem to be the most promising for such problems as water desalination, gases and ions separation as well as for DNA sequencing. In the present research the hexagonal boron nitride-based (h-BN) membranes with rectangular nanopores were examined for the first time in order to estimate their potential as water filter material. The nonequilibrium molecular dynamics (NEMD) simulations were performed to get theoretical estimates of ion rejection and water conductance of three model h-BN membranes. We introduced the terms “zigzag” and “armchair” for the first time to characterize the types of rectangular nanopores in two-dimensional materials with hexagonal packing of atoms. The results of NEMD simulations showed that a model membrane with rectangular armchair nanopores of 7.514 A width has an excellent permeability-selectivity efficiency including 100% salt rejection.

Confined in porous oceanic minerals, the subducted water alters physical and mechanical properties of host rocks, induces their super-hydration and thereby plays an important role in geodynamics. Under the extremal conditions of subduction zones, water can be trapped inside nanoscale slit-shaped pores of hydrophilic minerals as layered oxides/hydroxides. The structure and mechanical properties of water in such nanopores are quite different from those in normal bulk conditions. To understand how the nanoconfined water affects the properties of water-saturated rocks at extreme pressure conditions corresponding to subducting slabs, we use the atomistic molecular dynamics simulations. Considering a water-filled layered mineral MeII(OH)2, in which MeII is some divalent metal, we found two points of nanoconfined water phase transition in slit-shaped nanopore within pressure range 0.1–10 GPa: transformation from liquid phase to hexagonal close-packed (HCP) crystal at pressure 3.0 GPa and HCP to face-centered cubic (FCC) crystal transformation at 6.7 GPa. Moreover, the phase transformations of water in the nanopore of the mineral are accompanied by a stepwise reversible increase in the compressibility of water up to 1–1.5 orders of magnitude. Strong transient variations in the compressibility of confined water can cause significant difference in local values of compressive mean stress grow rate in heterogeneous subducting slab, thus contributing to localization of shear strain and initiation of dynamic rupture.

In the paper, we discuss an approach to the development of methods for managing seismotectonic deformation processes in a multiscale block-structured Earth’s Crust from the viewpoint of the concept of physical mesomechanics. To date, there are no convincing results of many year researches in the fields of earthquake prediction and prevention of the dangerous man-caused and tectonic earthquakes. Therefore, in recent decades, there has been an increasingly active search for new ways to solve the problem of seismic safety. The aim of our research team’s activity is to provide a scientific rationale for a multidisciplinary approach to reduce the excess level of shear stresses in the fault zones to a safe background level by “spending” it on mechanical destruction and thermal processes in rocks during aseismic and co-seismic slip. The authors summarize the main results of modeling of geological and geophysical processes in the field of preparation of different scale seismogenic events, as well as the results of complex man-made impacts on segments of seismically active faults. The data obtained on segments of different scale faults within the Baikal rift zone and Mongolia confirm the possibility of implementing such an approach. For the practical implementation of such a project at highly stressed fault zones, it is necessary to carry out vertical, oblique and horizontal multilateral drilling with an injection of fluids of different compositions in combination with vibro-pulse stimulations to achieve safe relaxation of shear stresses.

This paper presents a new approach to describe the mechanical behavior of semi-crystalline polymers, the plastic deformation of which is determined by their two-phase structure. To describe the plastic behavior of semi-crystalline polymers, a two-phase model is used. In the framework of this model, one phase is in a hard (crystalline) state, and the other in a soft (amorphous) state. The two-phase material is modeled by a single-phase homogeneous continuum based on the approximation of the effective medium. It is assumed that two infinitely close material points of the continuum are connected in series by elastic and viscous bonds, which corresponds to the Maxwell model. It is shown that, in this case, the Maxwell continuum is a pseudo-Euclidean space. Generalizing the definition of defects from a three-dimensional space to a four-dimensional pseudo-Euclidean space, we obtained a dynamic system of nonlinear, interrelated equations to describe the behavior of translational-type defects in the solid phase and dynamic defects in the amorphous phase. As an example of an application for these equations, the phenomenon of creep under uniaxial loading is considered. It is shown that the formalism of the proposed two-phase model makes it possible to describe creep phenomenon regularities, which correspond to both the aging theory and the flow theory.

The paper is devoted to comparative analysis of the capabilities of the most common models of interfaces which are used for simulation of multiphase materials. Influence of the parameters of these models on the microscopic mechanical properties of the metal-ceramic composites was also investigated. It was shown that the most effective way of explicit modeling of interphase boundaries are models of extended (wide) interface area. For example, models of homogeneous interface zones provide the opportunity to study influence of thermal conditions of composite material production and differenceы between the elastic constants and rheological parameters of different phases on integral properties of the composites. If interphase boundaries are characterized by gradients of elemental composition and defect structure at the transition from one phase to another, is the most adequate to use “gradient” models of the interface zones.

A liquid in a pore volume influences on a strength of porous permeable media, both brittle and elastic-plastic. Despite of the dilation of the latter, a pore pressure of a liquid can remain nonzero under constrained shear loading. In the result, a liquid pressure contribute into a stress-strain state of a medium, and, correspondingly, into a strength. On the other hand, a liquid pressure depends on transportation properties of a medium namely on porosity and permeability, where the latter is determined by a characteristic diameter of filtration channels in a solid skeleton. A superposition and interplay of filtration of a liquid and its compression in pores originates a dynamical distribution of a pore pressure in a bulk of material. The non-linearity and interconnectedness of the mentioned processes clearly demonstrate the necessity of application of numerical methods for a studying of strength properties of such permeable liquid-filled media. We have studied a dependence of shear strength of a water-filled elastic-plastic sample under constrained conditions in the framework of the hybrid cellular automaton method that represents a variation of a DEM with explicit account of a liquid in pores. An elastic-plastic sample has been mounted between purely elastic permeable blocks that moved in lateral direction with a constant velocity. There were periodic boundary conditions in lateral direction. In order to create an initial hydrostatic compression in a volume, a pre-loading was performed before shearing. The elastic blocks and the sample had the same values of porosity, permeability, elastic moduli etc. We varied the values of the shear rate, the value of hydrostatic compression, width of the sample and the permeability. We have found that the strength of the sample depends on a cooperation of the following processes: 1) increase of a mean stress in a medium under shear; 2) dilation of elastic-plastic sample after reaching a yield point; 3) mass transfer of a fluid in a pore volume of a sample and elastic blocks and 4) redistribution of a fluid pressure due to its mass transfer. The observed effects together with the results of numerical simulations allowed us to suggest a binomial dependence of shear strength of an elastic-plastic sample on permeability, loading parameters and geometry of a sample. The first term of this dependence describes the exponential decrease of strength of a sample due to the decrease of effective stiffness of the elastic blocks under outflow of a liquid into an excess pore volume of a sample. Note that the latter leads to the decrease of the degree of constraint. The second term characterizes the influence of filtration on an increase of effective stiffness of the sample due to the growth of pore pressure of a liquid. This, in turn, leads to the increase of the degree of constraint of the sample. The parameters of the given dependence represent the combinations of the values of loading, width of a sample, its physical-mechanical properties, including permeability, and physical mechanical properties of a liquid.

Molecular dynamics simulation of the bicomponent particle formation as a result of simultaneous electric explosion of copper and nickel wires is carried out. The influence of the internal structure of exploding metal wires and the distance between them on the dynamics of their dispersion, the size and phase composition of the formed particles is investigated. It is shown that the basic mechanism of particle synthesis is the agglomeration of smaller clusters, and the minor one is the deposition of atoms from the gas phase on the particle surfaces. The distribution of chemical elements is non-uniform over the cross section of the synthesized particles. The concentration of copper atoms in the subsurface region is higher than in the particle volume. Varying the loading parameters (temperature, distance between the wires) allows controlling the size and phase composition of the synthesized particles

This paper develops an approach to model the deformation and fracture of heterogeneous materials at different scales (including multiscale modeling) within a discrete representation of the medium. Within this approach, molecular dynamics is used for the atomic-scale simulation. The simply deformable distinct element method is applied for simulating at higher length scales. This approach is proposed to be implemented using a general way to derive relations for interaction forces between distinct elements in a many-body approximation similar to that of the embedded atom method. This makes it possible to overcome limitations of the distinct element method which are related to difficulties in implementing complex rheological and fracture models of solids at different length scales. For an adequate description of the mechanical behavior features of materials at the micro- and mesoscales, two kinds of models that consider grain and phase boundaries within the discrete element framework are proposed. Examples are given to illustrate the application of the developed formalism to the study of the mechanical response (including fracture) of materials with multiscale internal structure. The examples show that the simply deformable distinct element method is a correct and efficient tool for analyzing complex problems in solid mechanics (including mechanics of discontinua) at different scales.

This study shows the significant and nonlinear effect of the competition between dilation and fluid flow on the shear strength of constrained shear bands in fluid-saturated rocks. This effect is conditioned by the contribution of the pore pressure to the yield stress and strength. The pore pressure is controlled by the dilation of the pore space in the solid skeleton of the shear band during plastic deformation and by squeezing of pores in surrounding blocks by the dilating shear band due to the high stiffness of the host massif. A generalized equation has been derived to describe the dependence of the shear band strength on the ratio of strain rate to fluid flow rate.

A two-scale mechanical model of multiphase materials with the hard skeleton and different content of interstitial soft matter was developed within the framework of the formalism of movable cellular automaton method. In the paper, we numerically studied a particular example of such kind of materials, namely a heterogeneous porous composite with brittle matrix and plastic soft inclusions. The model was applied to study the fracture pattern and mechanical properties of mesoscopic samples with a linear distribution of the local porosity in the depth of the material under uniaxial compression. Simulation results showed the essentially nonlinear dependence of their elastic and strength properties on the degree of pore space filling. Depending on the sign of the gradient of porosity, the value of compression strength of partially filled samples can significantly increase or remain constant with increase in the volume fraction of filled pore space. It is shown that the combination of the parameters of pore structure, including a sign of the porosity gradient and the fraction of filled pore space, determines the shape of the main cracks and their localization.

Current geophysical experience shows that conventional measures proposed by the world scientific community to withstand seismic hazard, including various types of seismic zoning and earthquake prognosis, as well as costly earthquake-proof building, prove to be insufficient as they do not allow to avoid the destructive consequences of very strong earthquakes. Therefore, in recent decades, many geophysicists proposed new approaches to ensuring seismic safety. The present paper briefly discusses the results of geophysical studies, which are based on carrying out complex man-caused impacts on segments of seismically active fault zones. We discuss the prospects of formulation of a multidisciplinary approach to seismically safe reduce of the excess elastic strain energy in fault zones to a safe background level for hundreds of years. Potential realizability of the proposed approach is confirmed by the experience of small-scale tests in the fault segments of the Baikal rift zone. The key issues that inevitably arise during complex large-scale testing are considered by the example of the Arshan segment of the Tunkinsky riftogenic fault.

The paper presents the development of recently proposed kinetic model of dynamic mechanical behavior of brittle solids. The model uses the ideas of kinetic theory of strength to describe the inelastic deformation and fracture. The main feature of the modified dynamic model is the introduction of two relaxation times, which determine the patterns of inelastic deformation under dynamic loading, including the dependences of the values of the cohesion and strain hardening coefficient on the strain rate. These relaxation times have the meaning of a generation time of damage of the smallest ranks and a characteristic time of formation of a system of local damage and cracks of the greatest rank. The advantage of a developed dynamic model is the possibility of its implementation within different conventional models of inelasticity of brittle solids. In the paper we implemented the kinetic model within the classical “quasi-static” Nikolaevsky’s plasticity model (non-associated plastic flow rule with the plasticity criterion in the form of Mises–Schleicher). We verified the model and determined its parameters by the example of high-strength concrete. The developed dynamic model can be implemented within the framework of various Lagrangian numerical methods (including finite and discrete element methods) using an explicit integration scheme.

An approach to implementation of models of elasticity, plasticity and fracture of heterogeneous materials within the framework of discrete element method (DEM) is proposed. The approach is based on constructing many-body forces of element–element interaction within the formalism of simply deformable element approximation of generalized concept of DEM. Implementation of the approach is shown by the example of the movable cellular automaton method, which integrates the possibilities of DEM and cellular automaton methods. For correct modeling of inelastic deformation and failure of heterogeneous materials the dilatational non-associated model of plastic flow is implemented within the formalism of DEM. The examples are presented which illustrate correctness of the developed mathematical formalism and its usefulness in analysis of various problems in mechanics of discontinua.

We propose a microscale model of the main structural element (“bearing” layers) of kerogen-clay-carbonate-siliceous rocks of the Bazhenov formation. The model treats the rock as a composite material with inorganic clay matrix and different content of organic inclusions (up to 25%) and micropores filled with low-viscous fluid (light hydrocarbon fractions). A computer simulation of the mechanical behavior of representative samples of structural elements of the studied rock under triaxial compression was carried out using the hybrid cellular automaton method and a coupled mechanical model that takes into account the mutual influence of porous rock deformation and filtration of a pore fluid. It is shown that the mechanical behavior of the “bearing” layer of rock at side pressures that meet the characteristic conditions of occurrence is satisfactorily described by rock plasticity models with two-parameter flow functions.

The question about physically admissible velocity of dynamic crack growth is of significance to safety engineering as well as to earthquake dynamics. Recent researches including numerical simulations, experimental observations and the analysis of strong earthquakes have shown a possibility of propagation of shear cracks in supershear regime, namely at velocities comparable with dilatational wave speed. The present paper is devoted to the theoretical (numerical) study of some fundamental aspects of this problem. It is shown that development of a sub Raleigh shear crack is connected with a vortex traveling ahead of the crack tip at a shear wave velocity. The stress concentration area ahead of the crack tip revealed by different authors (Burridge, Andrews, Geubelle, Rosakis and others) is connected with this vortex. Acceleration of a shear crack towards the longitudinal wave velocity is concerned with formation of a daughter crack by the mechanism of shearing (the daughter crack is formed in the center of vortex). Analysis of sub Raleigh to intersonic transition has shown that development of shear cracks is self-similar and depends on dimensionless parameters.

Earlier the authors developed a discrete element based numerical model of dynamic mechanical behavior of brittle materials. The model is based on the concept of kinetic theory of strength. An important problem in the application of the proposed model to the study of features of dynamic response of real materials is lack of information about the dependence of model parameters on stress relaxation times (including time of fracture development). The present paper proposes an analytical approach to determining these dependencies for different brittle materials.