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In this paper, we carried out investigation of behavior of the material under loading condition identical those used in FSW using molecular dynamic method. The loading was modelled by a rigid rotating “tool” that movies along boundary between two grains. We considered pairing of two crystallites of copper, crystallites of copper and iron, and two crystallites of aluminum 2024. Analysis of the structure of the sample showed the intermixing and stirring of dissimilar atoms as a result the FSW tool pass at the inter-crystallite boundary. It was shown, that under certain condition of loading when tool passes there a region where atoms can occupying the original position of the crystal lattice. We also show influence of an additional oscillating impact applied to the moving tool on the structure of the resulting weld. The simulation results obtained can be used for understanding the processes realized under mechanically activated diffusion.

The paper is devoted to development of a new approach to study of friction stir welding (FSW) process on the mesoscopic scale. This approach is based on computer-aided simulation by movable cellular automaton (MCA) method. In the framework of developed formalism of MCA method the dynamics of the friction stir welding process of duralumin plates was investigated. It was shown that ratio of rotation velocity to velocity of translation motion of rotating tool greatly influences the quality of welded joint. Optimal choice of the ratio of these parameters could significantly decrease volume content of pores and microcracks in the welded joint.

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.

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.

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.

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.

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.