Vladimir A. Polyanskiy

Propagation of sound waves in stressed elasto-plastic material

Acoustoelasticity approach is a method of non-destructive testing and it is based upon the theory of propagation of ultrasonic longitudinal and transverse waves of different polarization in solids. This approach is able to uniquely determine the value of the principal stress in the case of no plastic deformation. An elastoplastic material with hardening is taken and the problem of propagation of a plane acoustic wave in a homogeneous prismatic elastic-plastic body that is uniaxially prestressed in the direction perpendicular to the wave propagation direction is solved. The sound velocities for the transverse and longitudinal waves are obtained for different approximations in terms of the first and second order of smallness. A strong dependence of the velocities from the hardening factor and component of the deviatoric stress tensor was detected. The study provides a number of closed-form expressions required for solving the practical problem of technical diagnostics of structures exposing plasticity.

Rheological Model of Materials with Defects Containing Hydrogen

A two-continua model is constructed which allows one to describe the kinetics of hydrogen in metals. The developed rheological model is appropriate for estimation of the hydrogen transition from mobile to bonded state depending on the stress-state relation and description of the localization of the connected hydrogen that results in the material fracture.

Surface effect of the waves of plastic deformation and hydrogen distribution in metals

The process of wave propagation in elastic-plastic media is accompanied by an oscillatory exchange between the potential and kinetic energy. The wave process decays rapidly if there is a large dissipation of energy in a continuous medium. In this connection, the paradox of the formation and propagation of plastic deformation waves under uniform deformation has not yet been unambiguously described. Several periods of the plastic deformation wave were observed in tested samples. The distribution of hydrogen is fully correlated with plastic deformation, namely, the larger the deformation, the higher the hydrogen content. This effect is explained by structural changes in the metal accompanying the plastic deformation. A mechanism for appearance of a surface plastic wave is proposed.

Acoustic anisotropy and dissolved hydrogen as an indicator of waves of plastic deformation

The method of acoustoelasticity is an ultrasonic method of nondestructive testing based on measurement of acoustic anisotropy, which is defined as the relative difference between the velocities of plane transverse ultrasonic waves of mutually perpendicular polarization. In contrast to the methods of tensometry, the method of acoustoelasticity allows one to obtain average values of mechanical stresses along the thickness of the material. Comparative studies of the distributions of acoustic anisotropy and concentrations of dissolved hydrogen were obtained for specimens from rolled commercial alloys in the case of large plastic deformations and after their destruction. The significant influence of microcracks on acoustic anisotropy was revealed. A new formula for the dependence of acoustic anisotropy on initial texturing, stresses, localized plastic deformations and microcracks is proposed. The theoretical model based on the concept of local surface microcracking was constructed. It allows us to explain the correlation between the distributions of acoustic anisotropy and hydrogen concentrations. Analytical expressions for the relation between the velocities of ultrasonic waves and components of the damage tensor were obtained. This makes it possible to evaluate the damage based on the anisotropy of the acoustoelastic properties of the material. The results of the investigation allow us to propose a new method for identifying the regions of localization of plastic deformations, microcracking and local zones with increased hydrogen concentration.

Application of Rheological Model of Material with Microdefects and Nanodefects with Hydrogen in the Case of Cyclic Loading

The paper deals with the example of application of the two continuum rheological model of materials with microdefects, nanodefects and solute hydrogen for calculation of stress and strain in cylindrical specimen under periodic loading. The model suggested allows one to relate the mechanical characteristics with the hydrogen concentration.The stability analysis of the system metal-hydrogen is carried out. The influence of parameters of the mechanical loading, hydrogen concentration and parameters of sorption and desorption of hydrogen from the surface of the internal defects (traps) of various nature on the system stability is performed.It is shown that influence of hydrogen can be considered as parametric instability of a continuous medium under mechanical deformation.This can be important during forming or plastic deformation of materials and nanomaterials containing hydrogen.