The computer-aided simulation of deformation and fracture of water-saturated elastic porous material with hybrid cellular automaton method

A method of numerical simulation of liquid-saturated porous media, that represents a combination of particle method and finite-difference method, namely, the hybrid cellular automaton method was proposed. It allows taking into account inelastic deformations, dilation and fracture of solid skeleton as well as the influence of pore pressure on the stress state of the skeleton and the redistribution of a liquid in filtration volume of porous medium. The method was applied to study the influence of viscous compressible liquid in pores of material on its strength and fracture. It has been shown that the strength of brittle liquid-saturated specimens depends on the material properties and the geometry of porosity, the physical-mechanical properties of the liquid etc. The latter shows the topicality of application of numerical methods to study and predict strength properties of fluid-saturated media under loading

Theoretical investigation of influence of pore pressure on mechanical response of gas-filled permeable materials

The paper is devoted to theoretical investigation of the influence of gas pore pressure on the characteristics of mechanical response of gas-filled permeable materials and media. Investigation was based on computer-aided simulation by hybrid cellular automaton method. Mechanical response of the model gas-filled samples of young brown coal under unconfined (in absence of constraint) and constrained conditions was investigated. The simulation results showed that increase of the pore pressure of the gas acting on the solid skeleton leads to decrease in materials strength. This is due to the fact that the gas pressure makes an additional contribution to integral pressure acting in volume of the loaded medium. Consequences of this are earlier beginning of plastic deformation and fracture of the material. It should be noted that in the constrained conditions decreasing of material strength with increasing gas pore pressure has more pronounced nonlinear character, in comparison with similar tests for unconfined samples. This is due to the fact that loading of constrained material is accompanied by its massive cracking and, consequently, by a grater decrease of the strength characteristics of the medium

Investigation of regularities of formation and propagation of elastic vortices in surface layers of materials under dynamic contact loading

On the base of computer-aided simulation by movable cellular automaton method regularities of formation of vortices in surface layers of materials under dynamic contact loading were investigated. It was shown that the dynamic contact loading leads to the formation of an elastic vortex in the area of contact interaction and its subsequent propagation in the volume of material. Direction of vortex movement essentially depends on the velocity of contact loading and value of the contact pressure, which are determined features of the interaction of the material surface and the counterbody (e.g. stress state of contact area)

Determination of the parameters of plasticity models of geological media on the base of computer simulation

The paper is devoted to theoretical investigation of peculiarities of inelastic deformation of porous brittle materials in constrained conditions. The study was based on computer-aided simulation by movable cellular automaton method. Analysis of the simulation results allowed to estimate values of some rheological parameters of porous brittle materials and to determine the limits of applicability of Mises–Schleicher equation for description of the inelastic deformation of such materials under axial compression in constrained conditions

Development of discrete element approach to modeling heterogeneous elastic-plastic materials and media

A general approach to realization of models of elasticity and plasticity of isotropic materials within the framework of discrete element method (DEM) is proposed in the paper. It is based on building many-body potentials/forces of discrete element interaction, which provide response of element ensemble correctly conforming to the response of simulated solids. Developed formalism makes possible realization of various rheological models in the framework of DEM to study deformation and fracture of solid-phase media of various nature

Simulation of the mechanical response of fluidsaturated porous medium with hybrid cellular automaton method

The connected physical-mechanical model of fluid-saturated porous medium, based on the coupling of particle method and net method, has been proposed. The model has been applied to simulation of the mechanical response of gas-saturated brittle material under uniaxial loading. An anomalous increase in strength and deformation capacity of samples in a certain range of pressure of gas in pores has been revealed. It has been shown that in this pressure range the destruction of the samples occurs with the formation of a large number of small fragments that can serve as a model of gas-dust emission into mine area

Investigation of dilatancy in block-structured geological medium on the base of movable cellular automaton method

The peculiarities of dilatancy processes in block-structured media that experience nonequiaxial compression under shear deformation are investigated using movable cellular automaton (MCA) method. For a characteristic of compression nonequiaxiality (also termed the degree of constraint) a dimensionless parameter – the lateral to normal pressure ratio in the deformation plane – used. The main objective of the work is to trace the sequence in which various dilatancy mechanisms are involved in deformation depending on the level of shear stress and degree of constraint. It is shown that in the block-structured medium an increase in the degree of constraint causes the dominating dilatation mechanism to change from slip of discontinuity surfaces to opening and expansion of pores. The dominating dilatancy mechanism changing because increasing the degree of constraint increases the threshold shear stress at which the slip is activated. Beginning with certain lateral pressures, the slip is impeded giving way to expansion of the pore space; however, the latter fails to provide so considerable volume change as the slip of contact surfaces does, and this decrease critical dilatation characteristics of the medium and, in particular, its dilatation coefficient and volume changing

Development of multiscale approach to modeling mechanical response of high-strength intermetallic alloys on the basis of movable cellular automaton method

On the basis of movable cellular automaton method (MCA) was developed a multiscale two-dimensional structural and rheological model of hard-strength intermetallic alloy Ni3Al. In this model, the intermetallic alloy is regarded as multiscale composite system. Developed approach takes into account the properties of grain boundaries, the characteristics of the geometry and internal structure of the grains and their size distribution. Internal grain structure of hard-strength alloy is constructed in the framework of MCA method using the algorithm of Voronoi tessellation. To simulate the processes of deformation and fracture of such complex systems by MCA method the two-dimensional model of elastic-plastic interaction of cellular automata is used. This model is based on the use of many-particle potentials/forces of interaction of cellular automata. An incremental theory of plasticity of isotropic medium with von Mises plasticity criterion was used to model deformation of intermetallic alloy. Radial return algorithm of Wilkins was adopted for this purpose. Twoparameter criterion of Drucker-Prager was used as fracture criterion in proposed model. When modeling of the mechanical response of hard-strength alloy peculiarities of its multiscale internal structure (the presence of subgrains in grains) at lower scales with respect to the considered one was taken into account implicitly using a specially developed multiscale approach. Verification of the developed model is performed by simulation of tests on the uniaxial tension of Ni3Al samples and comparing the simulation results with the experimental data. Comparison of the obtained “theoretical” loading diagrams with experimental data showed good qualitative and quantitative similarity. This indicates the adequacy of the developed model and the possibility of its use to describe the deformation and fracture of such complex heterogeneous systems

Development of a formalism of discrete element method to study mechanical response of geological materials and media at different scales

A general approach to realization of models of elasticity, plasticity and fracture of heterogeneous materials within the framework of particle-based discrete element method is proposed in the paper. The approach is based on constructing many-body forces of particle interaction, which provide response of particle ensemble correctly conforming to the response (including elastic-plastic behavior and fracture) of simulated solids. For correct modeling of inelastic deformation and failure of geological materials and media at "high" structural scales (relative to the scale of grains) an implementation of dilatational Nikolaevsky's model of plasticity of rocks within the framework of mathematical formalism of discrete element method is proposed. Perspectives of multiscale modeling of geological materials from grainrelated scale up to macroscopic scale within the same numerical technique (DEM) are discussed