Purpose. To evaluate the change in free energy in the transition from the nonequilibrium state of the rock to the equilibrium. This process implements the process of dynamic brittle fracture on the structural defects of the rock as a microinhomogeneous medium.Methodology. It included conducting, within the framework of statistical thermodynamics, a series of experimental studies on the density and velocity of propagation of longitudinal and transverse acoustic waves in sandstone samples under different loading conditions.findings. According to the experimental data on the velocities of propagation of longitudinal and transverse acoustic waves for a number of sandstones at different loading modes, the values of mechanical and thermodynamic parameters characterizing the state of rocks are established. A comparative analysis of the frequency dependences of free energy on the value of the Poisson ratio is carried out. originality. A model of a thermodynamic system is proposed that describes the energyactivated process of transition of rock from a nonequilibrium state to equilibrium during external perturbation by surface acoustic waves. The possibility of estimating the degree of slow dynamic destruction by the Debye temperature is revealed. The mechanism of dissipation of internal energy on structural defects of the system, with the transition of its part into thermal motion of structural elements, is substantiated.Practical value. The technique for investigation of thermodynamic state of nonideally elastic rocks by methods of nondestruc tive testing is developed. The correlation between the mechanical parameters of the rock and the characteristics of the process of its transition from the nonequilibrium state to the equilibrium is established.

No abstract

The paper deals with its own oscillations of a rectangular rod with a cross section of a rectangular shape. The method of determining real part of Young's dynamic modulus and tangent of mechanical loss of samples in the form of rods of a number of polymer materials by means of resonant vibrating-reed method are proposed. Experimental setup, algorithm and software for determining the amplitude of the sample oscillations are developed. The accuracy of measurements was determined and a comparative analysis of results was performed with data obtained by other methods.

The use of fractal and percolation approaches to the metal-filled polymer systems enables to analyze processes of their structure formation. The main aim of research paper is to define structural parameters and mechanical properties of metal-filled polyurethane systems based on results of ultrasonic study using fractal analysis and percolation approach. Polyurethanes auxetics filled with particles of iron (Fe), molybdenum (Mo) and wolfram (W) with radius between 0.3-1.0 µm are investigated. Polyurethane composites with polymer matrix are made of thermoplastic polyurethane synthesized from 4.4′-Methylen diphenyl diisocyanate, 1.4-Butanediol and Poly(tetramethylene ether)glycol with molecular weight 1500. Metal-filled polymer systems are obtained with the help of hot-pressing in T-p mode just after the components were all mixed. The results of acoustic research of investigated metal-filled thermoplastic polyurethane systems with 52% vol. Fe, 48% vol. W, 43% vol. Mo have proven to be with negative Poisson's constant. Based on percolation cluster model of metal-filled polyurethane auxetics their fractal dimensions and percolation indexes are distinguished. Usage of fractal-percolation ap

The process of resonance oscillations of a cantilever-fixed polymer rod with a rectangular cross section is considered. The values of the resonant frequencies of the own oscillations of the rod were obtained. The possibility of determining the real and imaginary parts of a complex dynamic Young's modulus of a polymeric rod at basic resonance frequency is shown.