Nonequilibrium processes in condensed media: Part 1. Experimental studies in light of nonlocal transport theory

Based on experimental research in shock loading of solid-state materials it is shown that among the important dynamic characteristics of the process, like spatial-temporal mass velocity profiles of shock waves, are the mass velocity variation, velocity defect, and structural instability threshold recorded in real time. Analysis of these characteristics depending on the strain rate, target thickness, and structural state of material demonstrates that conventional approaches of continuum mechanics fail to provide their adequate interpretation and simulation of shock wave processes. A new concept of shock wave processes in condensed media is proposed. The concept, being based on nonlocal nonequilibrium transport theory, allows describing the transition from elastic to hydrodynamic response of a medium depending on the loading rate and time. A nonstationary elastoplastic wave model is proposed for describing the relaxation of an elastic precursor and formation of a retarded plastic front during the wave propagation in a medium with regard to structural evolution. Analysis of the experimental data shows that the division of stresses and strains into elastic and plastic components is incorrect for shock loading.     

Defect-induced instabilities in condensed media

Some universal responses of condensed media to intense loads are studied. This behavior is attributed to the evolution of ensembles of mesoscopic defects (microcracks, microshears). It is shown that there exist several types of attractors which control the evolution of ensembles of defects under conditions of nonequilibrium transitions. The role of these transitions in the development of anomalies of the deformational behavior of solids and instabilities during fluid flow is discussed. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 714–721 (10 May 1998)     

Nonequilibrium processes in condensed media. Part 2. Structural instability induced by shock loading

In the first part of the work, we described our concept of shock wave processes, which is based on nonlocal nonequilibrium transport theory, and an associated mathematical elastoplastic wave model that allows for inertial properties, structural changes, and variation in mechanical properties of solid-state materials under shock loading. In the second part of the work, it is demonstrated that the energy exchange between the scales of dynamic deformation is defined by the relation between the characteristics measurable in real time: the mesoscale mass velocity variation and the mass velocity defect due to loss of the energy expended in structure formation. An internal criterion is found for the transition of a dynamically deformed material to structural instability.     

Cluster structure of condensed media

This paper presents the results of a theoretical study of cluster formation in condensed media for simple and multi-atomic liquids, as an example. A two-parameter function is proposed by the authors for the density of the probability distribution of clusters, which corresponds to a disordered condensed media, depending on the number of constituent particles. Using this function, the universal mean, most probable, and rms numbers of particles in clusters of noble gases, liquid metals, and some organic liquids were calculated. As well, the cluster component of total entropy for the substances under study was computed.     

Equation of state of condensed media

A new choice is proposed for the generating functional which is used to obtain an integral equation for the radial distribution function that is valid in the domain of dense fluids. The corresponding equation of state for giving the intramolecular potential in the form (r)r ^–s agrees in the case of dense fluids with the known Tait empirical equation of state. The Tait equation is extended to the high-pressure case. Processing the experimental data for water exhibits good agreement between the equation of state obtained and experiment in the pressure range from 10⁵–10⁹ Pa.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 43–47, December, 1981.     

Raman scattering in condensed media placed in photon traps

A new type of resonator cells (photon traps) has been worked out, which ensures the Raman opalescence regime (i.e., the conditions under which the relative Raman scattering intensity at the outlet of the cells increases significantly as compared to the exciting line intensity. The Raman scattering spectra of a number of organic and inorganic compounds placed in photon traps are studied under pulse-periodic excitation by a copper-vapor laser.     

A study of vibrational states in condensed carbon-based media

The spectra of the optical constants n(v) and κ(v) of a strongly absorbing object, graphite, having a high concentration and mobility of free carriers, are calculated by the methods of classical dispersion analysis. The problem of detection and identification of vibrational states of the substance against an intense nonselective absorption is considered. The calculated spectra of the optical constants of graphite are compared with the analogous data obtained from the spectrum of attenuated total internal reflection in the range of the vibrational E _1u mode of a quasi-single crystal of graphite, the Raman spectrum of the sample, and the background spectrum of graphite structures.     

Dynamic origin of the condensed state in real processes

The behavior of condensed systems losing equilibrium under an external action is considered. The interrelation of irreversible processes in such systems is studied under the conditions when this relation becomes nonlinear. The concepts developed here make it possible to analyze processes and to reveal self-organization mechanisms as examples in three dynamic effects: constant friction, resonance mode of thermoelastic martensite transformations, and chemical dispersion upon doping of metal alloys. A conclusion is drawn regarding enhancement of interrelation between micro- and macroprocesses required for optimizing external action in condensed systems.     

Transfer processes in fractal media

An irreversible process in fractal media involves coupling relation between the space and the time. The present note displays how the fractional derivation has to be introduced to describe this effect. As a result the law of the chemical diffusion to a fractal is given.     

A hard sphere model of chemical reaction in condensed media

We use the methods of hard sphere kinetic theory, projection operators and multiple time scale analysis to derive a formalism of chemical reactions in condensed media. Enskog type rates are found to be capable of explaining the primary salt and solvent effects but are valid for the special case of the slow reaction limit where the threshold energy does not depend on the proximity of third bodies and the smooth tail and mass do not change upon reaction. Rigorous diffusion limited laws may also be derived.