Ivan Panteleev

The physical basis of the effects caused by electromagnetic forcing in the intensity of geoacoustic processes

The results of theoretical and experimental investigations into the physical causes and mechanisms of the electromagnetic effects that modulate the intensity of the geoacoustic processes are presented. The peculiarities of this effect before strong nearby earthquakes are studied.

Nonlinear dynamics of the blow-up structures in the ensembles of defects as a mechanism of formation of earthquake sources

A statistical thermodynamic description for the evolution of the ensemble of defects in a geological medium is suggested for modeling the formation of the potential earthquake source. The evolution of the medium with defects is described in terms of two order parameters, the damage parameter and the structural scaling parameter, which are the unknowns in the evolution equations. Based on the obtained constitutive relationships, a mathematical model is constructed and the final stage of the earthquake source formation and propagation of the slow waves is numerically modeled. Our results can be interpreted as the model visualizations that render, in terms of a seismic process, the physical hypothesis implying the common formation mechanism of the defects (discontinuities) over a wide range of spatial scales.

Criterion for fracture transition to critical stage

AbstractWe have developed an analysis of data obtained in laboratory investigations of deformation of rocks by acoustic emission and X-ray microtomography. We found that defect accumulation occurs in fundamentally differing manners during loading. At first, defects are generated randomly and have a specific size determined by a typical structural element of a material (e.g., a grain in granite). Then the defects with sizes not dictated by the material structure are generated. The interaction between these defects gives rise to critical defects that are capable of self-development. In all probability, a sample breakdown results from the evolution of the ensemble of critical defects. We found that the fracture stages can be distinguished by the type of energy distribution function of the acoustic emission signals. At the first stage, the distribution is approximated by an exponential function, whereas the second stage is characterized by a power-law function that points to a self-organized criticality state...

Effect of the state of internal boundaries on granite fracture nature under quasi-static compression

Based on an analysis of the spatial distribution of hypocenters of acoustic emission signal sources and an analysis of the energy distributions of acoustic emission signals, the effect of the liquid phase and a weak electric field on the spatiotemporal nature of granite sample fracture is studied. Experiments on uniaxial compression of granite samples of natural moisture showed that the damage accumulation process is twostage: disperse accumulation of damages is followed by localized accumulation of damages in the formed macrofracture nucleus region. In energy distributions of acoustic emission signals, this transition is accompanied by a change in the distribution shape from exponential to power-law. Granite water saturation qualitatively changes the damage accumulation nature: the process is delocalized until macrofracture with the exponential energy distribution of acoustic emission signals. An exposure to a weak electric field results in a selective change in the damage accumulation nature in the sample volume.

Multiscale mechanisms of strain instability and damage localization under intensive loading

In-situ experimental data and structural analysis of recovered samples are used to support the multiscale modeling of dynamic strain localization and damage-failure transition as the precursors of adiabatic shear failure. New mechanism of adiabatic shear failure formation is proposed that links the multiscale collective behavior of typical mesoscopic defects (microshears) and generation of collective modes of defects responsible for characteristic stages of strain and damage localization under dynamic loading.

Structure of a Deformed Inhomogeneous Material on the Data of Acoustic Emission and X-Ray Computer Microtomography

Accumulation of defects at various stages of the deformation of a structurally inhomogeneous material (granite) has been studied using two nondestructive methods: acoustic emission (AE) and X-ray computer microtomorgaphy (CT). The quasi-static testing of cylindrical samples of a Westerly granite was carried out under uniaxial compression. The control of the defect formation was realized using the real-time monitoring of acoustic emission. For each sample under study, several steps of the loading and tomographic imaging have been performed. We have found that an exponential or power-law function of the energy distribution of the AE signals makes it possible to select a sample region, in which the system of defects has transited into a self-organized criticality state and large cracks have been formed. This result coincides with the data of the X-ray tomography Computer Microtomography.

Numerical simulation of artificial ground freezing in a fluid-saturated rock mass with account for filtration and mechanical processes

This study is devoted to the numerical simulation of the artificial ground freezing process in a fluid-saturated rock mass of the potassium salt deposit. A coupled model of nonstationary thermal conductivity, filtration and thermo-poroelasticity, which takes into account dependence of the physical properties on temperature and pressure, is proposed on the basis of the accepted hypotheses. The considered area is a cylinder with a depth of 256 meters and diameter of 26.5 meters and includes 13 layers with different thermophysical and filtration properties. Numerical simulation was carried out by the finite-element method. It has been shown that substantial ice wall formation occurs non-uniformly along the layers. This can be connected with geometry of the freezing wells and with difference in physical properties. The average width of the ice wall in each layer was calculated. It was demonstrated that two toroidal convective cells induced by thermogravitational convection were created from the very beginning of the freezing process. The effect of the constant seepage flow on the ice wall formation was investigated. It was shown that the presence of the slow flow lead to the delay in ice wall closure. In case of the flow with a velocity of more than 30 mm per day, closure of the ice wall was not observed at all in the foreseeable time.

Fragmentation of Mansurov granite under quasi-static compression

The fragmentation statistics was studied in the quasi-static compression experiments conducted on prismatic specimens of Mansurov granite. The statistical analysis showed that the cumulative fragment mass distribution for granite specimens is well described by a power law function, but the fragment number-sieve size distribution deviates from the power law in the range of are equal to about 1 mm. In order to explain this fact, we investigated the structure of fractured material (Computed Tomography and microstructures study in thin sections). A sharp increase the number of grains in the range of size from to 0.5 mm to 1 mm and a change in the fragment shape (from splinter to oval) allow us to suppose that there is an addition fracture mechanism associated with disintegration of feldspar and amphiboles grains.

Numerical simulation of deformation and failure of orthotropic composite materials

This paper presents experimental and theoretical study of the mechanical and strength properties of orthotropic composite materials. The anisotropy of a composite material is caused by its manufacturing method. Fiberglass composites based on epoxy resins (laminates) are investigated. The material is considered to be orthotropic, and the orthotropy axes coincide with the characteristic lines of fiber stacking. The aim is to develop a mathematical model of deformation and fracture of composite materials under quasi-static and dynamic loadings. The developed mathematical model is adapted to the Abaqus finite-element simulation software, which allows numerical simulation based on the original constitutive relations of an orthotropic medium taking into account the accumulation of damage. The paper compares experimental results and numerical simulation for flat specimens of an orthotropic composite material in the case of uniaxial deformation. Adequate results on the modeling of deformation and fracture of orth...

Identification of fracture mechanisms of fiberglass laminate based on the acoustic emission data

This work is devoted to classification of the acoustic emission pulses on the base of cluster analysis of acoustic emission data registered during quasistatic uniaxial tensile of fiberglass laminate samples. There were established characteristic parameters and stages of acoustic emission for each type of fracture: matrix fracture, fiber fracture, fiber/matrix debonding, delamination.