E. V. Shilko

Movable cellular automata method for simulating materials with mesostructure

Mathematical formalism and applications of the movable cellular automata (MCA) method are presented for solving problems of physical mesomechanics. Since the MCA is a discrete approach, it has advantages over that of the finite element method (FEM). Simulation results agree closely with the experimental data. The MCA approach cab solves mechanical engineering problems ranging from those in material science to those in structures and constructions. Computer simulation using MCA can also provide useful information in situations where direct measurements are not possible.

METHOD OF MOVABLE CELLULAR AUTOMATA AS A TOOL FOR SIMULATION WITHIN THE FRAMEWORK OF MESOMECHANICS

ConclusionThe proposed MCA method is based on mesomechanics of heterogeneous media [4, 5, 9]. It is connected first with the ability to describe the material as a set of structural elements of deformation [9]. The role of the structural unit in the MCA method is played by the element (movable cellular automaton). The expressions of interparticle interactions used, as well as the rules of changing the state of the elements, allow us to simulate a wide range of phenomena including melting, chemical reactions, and phase transformations. The characteristic size of the element and its properties are defined based on the features of the model constructed in the framework of mesomechanics as described in [9]. Therefore the MCA method as a computational technique allows us to realize the principles of mesomechanics when simulating material response to external loading of different types. This method is highly recommended in computer-aided design of new materials.

Dynamic vortex defects in deformed material

The paper studies the generation and evolution of dynamic vortex structures in a material on different structural scales. It is shown that the generation of dynamic vortex structures can be the main accommodation mechanism in a material under external mechanical loading. On the microscale, these structures can provide inter-granular sliding and grain boundary migration with anomalously high rates. On higher structural scales, their evolution can be the main process responsible for nucleation and propagation of cracks, fragmentation of material, formation of a “quasiliquid” layer in friction pairs, etc. The data and conclusions derived from the study are confirmed by numerical calculations for different types of materials in the framework of molecular dynamics and movable cellular automaton methods.

Effect of dynamic stress state perturbation on irreversible strain accumulation at interfaces in block-structured media

The paper studies how the stress state of the interface between structural elements in a block-structured medium affects its deformation response to dynamic loading. It is shown that the normalized shear stress and mean stress are the major factors that determine the deformation response of the interface. We propose to describe the dependence of the value of induced irreversible displacement at the interface on the normalized shear stress using a logistic function. The central point of this function is the point of transition from the quasi-elastic to quasi-plastic stage of the interface shear deformation. The obtained empirical dependences are important for understanding the mechanism of irreversible strain accumulation in fault zone fragments and, particularly, for the development of an earlier proposed approach to estimate the characteristic level of active shear stresses in separate tectonic fault regions.

The features of fracture of heterogeneous materials and frame structures. Potentialities of MCA design

A new promising numerical method named movable cellular automata (MCA) is described. Because this approach is based on the discrete concept, in contradistinction to FEM-based software, the software based on the MCA concept has a few clear advantages. The main one is connected with modeling of real fracture process. The MCA method has been successfully used for modeling dynamic loading of heterogeneous materials and structures. The results of simulations agree closely with the experimental data. The results show that the MCA approach could be really useful to solve a lot of civil engineering problems from materials to constructions. Special software has been developed on the basis of this method. Due to its potentially unique abilities, the MCA method could be considered as a breakthrough in numerical techniques and a new tool of engineering mechanics.

Computer-aided examination and forecast of strength properties of heterogeneous coal-beds

One of the modern and perspective applications of computational mechanics is investigation of complex multiphase media containing components in different aggregative states. Striking examples of multiphase media are coal-beds, soils, geological medium and so on. In the present paper the new method for simulation of response and fracture of multiphase media, the hybrid cellular automaton method, is proposed. Developed approach was applied for computer-aided simulation of response and fracture of lignite under complex boundary conditions imitating real-life environment in coal beds. Simulation results show that presence of constrained boundary conditions can lead to change of lignite fracture regime in the range from brittle to quasi-viscous. In the case of hard boundary conditions increase of surrounding material hardness leads to transition from brittle fracture of fined detritus to degradation regime, which is characterized by generation and accumulation of numerous damages. As a result at slump of lateral pressure (in practice this situation is realized during mining or digging) fine detritus can demonstrate explosion-like fracture. In the case of boundary conditions realized by means of applied force (this type of boundary conditions is the most close to real conditions in coal beds) the vice versa dependency for fined detritus is observed. Here explosion-like regime is observed at lateral pressure slump in the case of soft surrounding material. Proposed hybrid cellular automata concept can be efficiently used for solving various geo-mechanical, biological, engineering and materials science tasks, which consider heterogeneous multiphase objects.

Three-dimensional movable cellular automata simulation of elastoplastic deformation and fracture of coatings in contact interaction with a rigid indenter

The paper considers 3D movable cellular automata (MCA) models of contact interactions involved in nanoindentation, sclerometry, and tribospectroscopy. The system under study is a titanium substrate with a harden coating. The substrate and coating materials are both described in the elastoplastic approximation. It is shown that the MCA method of numerical simulation provides correct description of the contact interaction of elastoplastic materials under different types of loads with explicit account for fracture. The possibility to detect damages in ma surface layers from friction force estimates is assessed.

Influence of phase interface properties on mechanical characteristics of metal ceramic composites

The paper reports on theoretical study to elucidate the influence of geometric (width) and mechanical characteristics of phase interfaces on strength, ultimate strain, and fracture energy of metal ceramic composites. The study was performed by computer simulation with the movable cellular automaton method and a well-developed mesoscale structural composite model that takes explicit account of wide transition zones between reinforcing inclusions and the matrix. It is shown that the formation of relatively wide “ceramic inclusions-binder” interfaces with gradual variation in mechanical properties allows a considerable increase in the mechanical properties of the composite. Of great significance is not only the interface width but also the gradient of mechanical properties in the transition zone. The presence of defects and inclusions of nano- and atomic scales in interface regions can increase internal stresses in these regions, induce a steep gradient of mechanical properties in them, and hence decrease strain characteristics and fracture energy of the composite.

Hybrid cellular automata method. Application to research on mechanical response of contrast media

In the work, a hybrid cellular automata method was developed to study behavioral peculiarities of heterogeneous materials and contrast media. The method is a combination of two approaches: classical and movable cellular automata methods. The method was verified through comparing simulation data on sorption of carbon dioxide in lignite and corresponding experimental data provided by researchers from Velenje Lignite Mine (Slovenia). The obtained estimates of model parameters were used in numerical simulation of the gas phase on the strength and fracture of lignite samples. It is shown that the presence of the gaseous atmosphere even of pressure 0.1 MPa changes the effective strength of the lignite sample and the character of their fracture. The developed method can be used to study behavioral peculiarities of complex multicomponent media such as coal beds in mine zones.

Physical modeling of seismic source generation in failure of fault asperities

A series of full-scale experiments was performed to study the influence of impact loads on the parameters of seismic vibrations initiated in variable friction. The study was conducted on a test setup Tribo which is a movable concrete slab modeling an allochthon on a rough plane of the Angara fault segment in Baikal region. Contact interactions of asperities in the slip zone were recorded using strain and load measuring equipment and four seismic stations Baykal-7HR widely used for recording earthquakes. The proposed physical modeling method and obtained results can be of interest for the development of new physical models of differently scaled sources of seismic energy dissipation in tectonic faults and can be useful for seismological studies, related data interpretation, and improvement of extended forecast of rock bursts and earthquakes.