Home – Home – Jornals – Combustion, Explosion and Shock Waves 2015 number 6

A method for identification of material parameters of the constitutive relations of elastoplastic and viscoelastic deformation of isotropic and composite materials is developed. The method is based on minimizing the functional of the residue of results of numerical and experimental analysis of unsteady deformation of structural elements made of examined materials. The method is tested, and prospects of its application for determining material parameters of viscoelastic and elastoplastic models of nonlinear deformation of cylindrical metal-plastic shells under explosive loading are demonstrated.

Results of an experimental study of properties of joints obtained by using different regimes of laser welding of the 1424 alloy (Al-Mg-Li) are reported. The strength and structure of the welded joints are determined. The influence of various types of welded joint straining on its strength is studied. It is demonstrated that the joint strength increases in the case of plastic straining.

A method of the numerical solution of nonlinear unsteady problems of axisymmetric elastoplastic straining of shells of revolution with allowance for torque loading at high strains is proposed. The method is based on the geometrically nonlinear theory of the Timoshenko shells and the plasticity theory with due allowance for combined isotropic and kinematic hardening. The problem is solved with the use of the variational difference method. Results of numerical and experimental investigations of elastoplastic straining of cylindrical shells under proportional and sequential kinematic tensile and torque loading are reported.

A mixed boundary-value problem for a parabolic equation of heat distribution in a layer is considered. Ggradient is specified in one region of the boundary, and temperature in the other. It is assumed that away from the initial conditions, the process is established in time and the temperature decreases slowly and exponentially and then increases. We study temperature localization in one of the regions, and the conditions and consequences of localization in the other region at various stages of temperature change. An analogy is drawn between the temperature distribution pattern in the layer and some climatic events.

An axisymmetric problem of high strains in a spherical lead shell enclosed into an aluminum ``spacesuit" under the action of pulsed loading is considered. The shell straining is described with the use of equations of mechanics of elastoviscoplastic media in Lagrangian variables, and the kinematic relations are determined in the current state metrics. Equations of state are taken in the form of equations of the flow theory with isotropic hardening. The problem is solved numerically by using the variational difference method and the ``cross" explicit scheme of integration with respect to time. The influence of the yield stress as a function of the strain rate on changes in the shell shape is studied for different values of loading. The calculated final shape and residual strains are demonstrated to be in good agreement with experimental data.

Results of a series of inverted laboratory experiments on the normal impact of spherical bodies onto targets made of wet sand (with humidity of 10$\%$) and water-saturated sand (with humidity of 18-20$\%$) placed into cylindrical metallic containers are reported. Experimental data are compared with results calculated by a modified Godunov difference method. Changes in the forces of resistance to penetration at different stages of the impact interaction process are analyzed, and the influence of humidity and granulometric composition of sand on the maximum values of forces at different impact velocities is studied. The maximum force of resistance for sand with 20$\%$ humidity is found to be smaller by a factor of 1.5-2 than that for dry sand.

Results of an experimental study of the behavior of St.3, 20Kh13, and 08Kh18N10T steels under static and dynamic loading are reported. The influence of the strain rate and temperature on characteristics of strength and plasticity is studied. Based on the data obtained, the parameters of the Johnson-Cook model are determined. This model is used in commercial software to describe the yield surface radius as a function of loading parameters. The adequacy of the identified model is verified in a series of special test experiments.

This paper considers a homogeneous isotropic elastic body bounded by concentric spheres and acted upon by axisymmetric unsteady volume forces. Displacement fields are determined using series expansions in Legendre and Gegenbauer polynomials, Laplace transforms in time, and integral representations with kernels in the form of Green's functions. Explicit formulas for the Green's functions are constructed that allow accurate determination of the originals. Examples of the calculations are presented.

A mathematical model is developed within the framework of equations of damaged medium mechanics to describe the processes of viscoplastic straining and damage accumulation in structural steels with allowance for fatigue and creep of the material. A model of damage summation due to interaction of low-cycle fatigue and creep of the material is proposed. Material parameters and scalar functions of equations of mechanics of damaged media are determined. Viscoplastic straining and fatigue-induced damage accumulation in 08Kh18N10T and 12Kh18N9 are studied numerically, and the data obtained are compared with available results of physical experiments.

The distribution of the energy of a piezoelectric actuator between normal modes (Lamb waves) as a function of the source parameters and frequency is studied by solving the dynamic contact problem of the interaction between a flexible piezoelectric patch and a flexible elastic substrate with explicit representations for the excited traveling waves. Zones of the maximum and minimum energy of the fundamental modes are determined in the “oscillation frequency-piezoelectric patch width” plane.

A two-dimensional model of an anisotropic crystalline material with cubic symmetry is considered. This model consists of a square lattice of round rigid particles, each possessing two translational and one rotational degree of freedom. Differential equations that describe propagation of elastic and rotational waves in such a medium are derived. A relationship between three groups of parameters is found: second-order elastic constants, acoustic wave velocities, and microstructure parameters. Values of the microstructure parameters of the considered anisotropic material at which its Poisson's ratios become negative are found.

A locally equilibrium model of mechanodiffusion which comprises a coupled system of motion equations for an elastic body and a mass transfer equation is used to solve the two-dimensional nonstationary problem of elastic diffusion for an isotropic one-component layer. The solution is constructed using Fourier series, Laplace time transforms, and Fourier transforms for the spatial coordinate. The Laplace transform originals are found analytically, and the Fourier transforms are inverted by quadrature formulas.

This paper describes the results of experimental studies on penetration of cylindrical projectiles into concrete and reinforced concrete at impact velocities reaching 0.5 km/s. An algorithm is proposed for calculating the depth of penetration of a projectile, making it possible to find the depth of penetration of high-strength steel projectiles with a mass of up to 13.5 kg into concrete on the basis of measurements of the specific work required to remove concrete using projectiles with a mass of up to 8 g.

This paper describes the dependence of the solution of the problem of equilibrium of a Timoshenko plate and the total energy functional of the plate on the surface perturbation, which is an oblique crack. The nonlinearity of the problem is caused by the boundary conditions in the form of inequalities (conditions such as the Signorini conditions), which simulate mutual nonpenetration of the opposite crack faces. The continuous dependence of the solution of the problem on the perturbation of the crack length is established. A formula for the energy functional derivative of the perturbation of the crack length is obtained.

Homogeneous and two-layer half-spaces consisting of an anisotropic elastic, isotropic viscoelastic, or poroelastic material are considered. The Kelvin-Voigt model and the model with the Abel kernel are used as models of the viscoelastic material; the poroelastic material is studied within the framework of the model of the compressible Biot material. The case where the half-space contains a cavity is also considered. Propagation of surface waves is studied by the boundary element method. The numerical solution involves the method of collocations for a regularized boundary integral equation.

A model taking into account finite deformations is constructed for the behavior of a shape memory polymer which undergoes a transition from the highly elastic to the vitreous state and back during deformation and temperature change. The obtained relations are tested on problems which have experimental support.

The axisymmetric contact problem of sliding of two solid parabolic indenters on a viscoelastic half-space with constant velocity is considered. Shear stresses modeling the adhesive component of the friction force act in the contact area. The model of the foundation material is described by an integral operator with an exponential kernel characterized by one relaxation time. The problem is solved by the boundary element method. The dependences of the contact characteristics on the sliding velocity, the normal load, and the distance between the centers of the indenters is analyzed. The results can be used to study the effect of the roughness elements modeled by two indenters on the contact characteristics and the deformation component of the friction force.

The influence of boundary conditions on the fracture of brittle geomaterial in the stress concentration zone under biaxial loading with account for the size effect is theoretically and experimentally studied. The calculation results are compared with the experimental data.

The linear plane problem of oscillations of an elliptic cylinder in an ideal incompressible fluid of finite depth in the presence of an ice cover of finite length is solved. The ice cover is modeled by an elastic plate of constant thickness. The hydrodynamic loads acting on the body are determined as functions of the oscillation frequency and the positions of the cylinder and plate.

The unsteady isothermal flow of a dense layer of a granular medium around an obstacle in a plane channel is modeled using the momentum transfer equations for an incompressible viscous liquid medium based on the slip of the medium at the walls. The validity of this approach is tested by comparing the calculated and experimental data for the flow of a highly concentrated granular medium with high flowability. The effect of periodic change in the flow rate of the granular medium over time in the inlet section of the plane channel on the unsteady distributions of the velocity and temperature fields is studied.

A method is proposed to determine the moduli of thin ferroelectric films subjected to forced deformation due to the mismatch between the crystal lattice sizes of the film and substrate materials and the difference of their thermal expansion coefficients. Models of single-crystal films of barium titanate are studied using the eighth-degree Landau thermodynamic potential. It is shown that in the considered range of forced strain of the barium titanate film, three main states exist: a tetragonal phase ($c$ phase) of 4mm symmetry with spontaneous polarization directed along the normal to the film plane; an orthorhombic phase ($aa$ phase) of 2 mm symmetry with polarization oriented along the diagonal plane of the film; monoclinic phase ($r$ phase) of $C_\rm m$ symmetry with the intermediate direction of polarization. All phases are separated by the lines of transitions of the second kind. Dependences of the elastic, electric and piezoelectric moduli on the magnitude of forced strain are plotted. It is shown that at the phase boundaries there is an anomalous change in the constants of the ferroelectric film and in the region of existence of the $r$ phase, some moduli reach extreme values.

The combustion chemistry of formaldehyde in fuel-rich flames has been studied by numerical modeling and sensitivity analysis. It has been shown that the wide flammability limits of CH2O air mixtures are due to features of the combustion chemistry of formaldehyde at high equivalence ratios rather than to the superadiabatic temperature effect. In this case, the thermal decomposition reaction of hydrogen peroxide H₂O₂ plays a key role in the conventional branching reactions.

This paper is devoted to methods of estimating the combustion regimes of gaseous fuel in vortex chambers of various designs in the presence of a bed of inert particles in the chamber, which rotate with the gas flow. A simple geometric criterion for determining the possibility of fuel combustion in the particle bed without the formation of a flame above the bed is proposed.

This work is an experimental and theoretical study of the dependence of normal flame velocity in polydisperse aerosuspensions of aluminum particles on the parameters of the particle size distribution function. It is shown that the velocity decreases with increasing dispersion of the distribution function as a result of reduction of the specific reaction surface.

Self-heating processes in binary homogeneous mixtures are studied based on the analysis of phase trajectories on the heating rate–temperature plane. The proposed approach allows determining the characteristic regions of exothermic reactions in the parametric diagram of the Todes criterion versus the Semenov criterion. Generalized strict criteria for the degeneration of thermal explosion are determined for reactions with low activation energy and reactions with a low thermal effect for any reaction orders. An approximating formula describing the dependence of the Todes criterion on the Semenov criterion is derived for calculating the critical conditions of thermal explosion up to its complete degeneration for reaction orders higher (or equal to) one. A criterion for the applicability of the classical thermal explosion theory as a special case of the proposed model is found. A diagram of the critical parameters in the introduced new variables is considered to predict and control the self-heating kinetics of mixtures.

The effect of sodium hydrogen carbonate and ammonium chloride on the combustion of iron aluminum thermite in air at atmospheric pressure is experimentally studied. The effect of salt additives on the average linear velocity of combustion, the relative yield of the metallic phase in the ingot, and the relative weight loss during thermite combustion are investigated. The concentration flammability limits of the mixtures under consideration are determined.

This paper presents the results of a study of the transition from layer-by-layer to convective combustion and to explosion for charges of advanced high-density explosives in a constant-volume chamber at a pressure of up to ≈60 MPa. Approximation of the results of the experiments with good correlation revealed a common parameter for explosives that characterizes the kinetics of convective combustion and made it possible to rank explosives according to their capability of transition from combustion to explosion. The results can be useful for computational modeling of explosion under accidental heating conditions.

This paper presents a physicomathematical model for the combustion of N powder which takes into account chemical reactions in the condensed and gas phases. On the burning surface, boundary conditions (coupling conditions) are specified. Results of calculation of the burning rate of N powder at constant pressure are in good agreement with available experimental data. The extinction of combustion of N powder by a sharp pressure drop pressure is simulates. Calculations of the boundary values of the degree and rate of pressure drop at which extinction of N powder occurs are in good agreement with published data of measurements.

The article analyzes the relationship of philosophical views of Aristotle and modern scientific ideas about the universe. The author argues that the physical world is invisible transcendental «beginning» and that the Aristotelian model of the universe can be the basis for the formation of future science.

The accepted assumptions in the history of development of logical semantics on the basis of opposition of universalists and model-tradition traditions are investigated. Formation of model-theoretical approach in connection with a problem of a definability of semantic concepts is in detail lit. The role of the implicitly accepted by A. Tarsky comes compositionality principles to light, its role in receiving result about inexpressibleness of concept of truth of natural languages is characterized.

The article shows the limited value of the deductive-nomological formalization for the explanation and understanding of natural phenomena. The formalization uses theoretical laws of nature, which very often have the status of ceteris paribus laws. Сontemporary philosophy of science uses the conceptions of Cartwright, Morgan and de Regt as an alternative to Hempel’s formalization. Our research demonstrates the adequacy of these conceptions for the explanation the phenomena and understanding of used theories. These conceptions use models rather than laws, where the model is the result of synthesis of a modified theory and data representing the phenomena under study.

The modern stage of the science development is characterized by two opposing trends: specialization, leading to the differentiation of the methods and approaches, and unification or standardization of methods, making them more universal. The latest trend provides the opportunity to unify knowledge as universal techniques make it possible to use them more widely. The application is accompanied by the transfer of universal techniques in a wide range of ontological and epistemological assumptions that underlie these practices, which contributes to the development of a universal ontology of the physical picture of the world.

The paper deals with the nature of mathematical concepts, genesis of natural numbers and the temporal structure of consciousness. We analyze the arithmetic model of time and propose a new geometrical model of bundle time which is based on the hypothesis of independent time dimensions corresponding to external linear time and internal cyclic one.

In the article are briefly shown the epistemological bases of cosmology, which became the first step toward the idea of the plurality of peaces and unification of fundamental physical theories. Thesis is based, that all studies in this region of cosmology rest originally on the ruling fundamental physical theories, and, first of all, to the general theory of relativity, which has several versions of the solution of its equations. But empirical data allow different theoretical interpretations of these solutions that it gives metaphysical nature to such ideas and makes with their object of philosophic methodological analysis. This fact is caused by the fact that they cannot be falsifitsirovany even in the case of the absence of mathematical and logical contradictions.

Awareness of self-awareness is a fundamental cognitive property of human beings. This means that awareness of self-awareness could be naturalized as specific functional mental state of human brain. Nature of reflection as real mental state is social one. Evolution of reflective forms of mind could be explained through evolution epistemological standpoint as a result of social reflective games. Organisms have an ability to grasp opponent’s reflective range and to detect epistemic lie by their behavior and external physiological data. Probably this is possible due the evolution of empathy phenomena caused by mirror neurons.

The concept of consciousness is considered through its relation to unconscious mental processes, brain activity, and behavioral automatisms. Impossibility of consciousness ontology construction with consciousness being detached from unconscious work of the mind is shown though fallacy of some reductive and nonproductive views on consciousness.

A curious instance of utilization of algebraic terminology in Hippolytus’ ( Elenchos I 2, 9-10: dynamis, cubus, dynamocubus , etc.) indicates that a relatively advanced arithmetic originated in works of such mathematicians as Heron and Diophantus, for some reason, aroused interest in Platonic and Pythagorean circles. Indeed, if we were to look for an example of an “ideal” Pythagorean, Diophantus would certainly qualify: he wrote a book on such a popular Pythagorean subject as polygonal numbers, transformed traditional arithmetic, and created a new theory of number; in a word, he did things a Pythagorean is supposed to do. It is no secret that Pythagorean numerology is not very useful from a mathematical point of view. What if an unknown Pythagorean (Hippolytus’ source) decided to translate the standard Pythagorean theory into the language of higher mathematics of his time? It is as if asked to define number I were to indulge in axiomatic set theory. Besides, the text has clear implications for the dating of Diophantus. Textual observations allow us to entertain the idea that Diophantus as the philosophus Pythagoricus was known and used in the Neopythagorean and Platonic sources from the second, and, possibly, the first century AD. Moreover, if he, as it seems, authored an introductory work on arithmetic, he may be set in a series with such persons as Eudorus, Cleomedes, Moderatus, Nicomachus, and Theon of Smyrna as a fully fledged contributor to the development of the Neopythagorean movement, perhaps to be placed somewhere between Eudorus and Nicomachus.

The review of approaches to the problem of unity of knowledge in the history of philosophical thought made. Performances philosophers from antiquity to modern times and the varieties of reductionist and synthetic models of the unity of knowledge since the philosophy of positivism are considered. Based on the review is concluded that there are several basic approaches to the problem of the unity of knowledge. The approaches can be classified by the ontological (the possibility of the unity of the world) and epistemological (the possibility of reducing / combining elements of the world) grounds.

The author demonstrates the dynamics of the attitude of the expert community to the problem of adaptation and integration of migrants on the example of changes in the migration legislation of the Russian Federation, the emergence of new educational practices. In the article the problems and the prospects of educational space are presented as a part of interaction between the «newcomers», representatives of ethnic groups, and the «locals», the representatives of the host community, and are considered in two aspects. In the aspect of adult education we are talking about the need to improve the legal framework and practices of certification of foreign citizens to obtain a patent for work in Russia. In the aspect of the education of migrant children we are talking about the difficulties faced by the education system and groups of schools with the multinational structure of pupils. The presented material contains the findings of sociological research aimed at identifying the strategies of mutual adaptation of migrants and the host community.On the basis of analysis of the statistical data obtained from the survey of ethnic migrants from neighboring countries and representatives of the host community, several significant conclusions are made. In the sphere of interpersonal relations it is obvious that ethnic migrants are striving to reduce the distance with the host community, but the «locals» remain indifferent to their efforts. Eventually, adaptation measures are necessary to both parties: migrants and the host community. The activity of state structures (including FMS), aimed at the incorporation of immigrants from neighboring countries into the structure of Russian society, is insufficient. The efforts of scientific and pedagogical intelligentsia will not yield a positive result unless on the regional and municipal levels there are formed expert network undertaking ethnosocial monitoring. Besides, appropriate programs are necessary to facilitate the adaptation of children of different nationalities to the educational space, cooperation between the two categories of the population in the framework of territorial public self-awareness in the media, including in terms of the presentation of the objective criminal statistics, both about the ones which are committed by migrants and in relation to them. These measures should be implemented in a comprehensive manner and focused not only on migrants, but also on the host society.

As the title implies, the article describes the content of the concepts of imagology and artistic imagology. Also, the authors give a description of the concepts of travelogue and the most successful of them are indicated. The authors’ attention is given to the development of artistic imagology as a way of learning a foreign culture. This aspect is based on the example of L. Stern’s «Sentimental travel». This area is also complemented by the consideration of the travelogue of French Marquis Astolphe de Custine «Russia in 1839». The authors come to the conclusion that imagology reflected in the travelogues gives a visual perception of the people and the country, their culture and lifestyle.