I. Yu. Belyaeva

Nonlinear Interaction of Acoustical Waves Due to Cracks and Its Possible Usage for Cracks Detection

An interaction of a CW acoustic wave and a powerful acoustic pulse due to nonlinear properties of a crack-type discontinuity in a solid is considered. Characteristics of nonstationary variations of the reflected wave amplitude and the phase of the transmitted wave, which are induced by the powerful pulse, are determined. The effects should allow one to distinguish cracks from other scatterers and can be used as a base of a new method of crack detection and positioning. Demonstrative signal estimates based on two simplified crack models are presented.

The equation of state of a microinhomogeneous medium and the frequency dependence of its elastic nonlinearity

In the framework of a rheological model, a nonlinear dynamic equation of state of a microinhomogeneous medium containing nonlinear viscoelastic inclusions is derived. The frequency dependences of the effective nonlinear parameters are determined for the difference frequency and second harmonic generation processes in the case of a quadratic elastic nonlinearity. It is shown that the frequency dependence of the nonlinear elasticity of the medium is governed by the linear relaxation response of the inclusions at the primary excitation frequency, as well as by the relaxation of the inclusions at the nonlinear generation frequencies.

Comparison of linear and nonlinear elastic moduli for reservoir rock by use of a granular medium model

The variations of linear and nonlinear elastic parameters as a function of initial stress and material structure are considered using a model of a granular medium with fluid pore filling. Examples of such variations for some geological conditions interesting for seismoprospecting are presented. It is demonstrated that the nonlinear parameter may be used in exploration seismology as a much more sensitive characteristic compared with conventionally exploited linear moduli.

Nonlinear Scattering of Acoustic Waves by Discontinuity-like Defects in Application to Crack Detection

Nonlinear sound scattering into higher or combination frequency harmonics on a crack-type dis continuity in a solid due to the intrinsic nonlinearity of the crack is considered. Characteristics of the nonlin early scattered sound are estimated, taking into account the micro-roughness of crack surfaces. Possibilities of the effect of usage for crack detection are discussed, comparison with conventional linear approaches is performed, and the main expected advantages of the nonlinear methods are pointed out.

Nonlinear combinational sound scattering by discontinuity‐like defects in solids and its possible usage for crack diagnostics

One of the important problems in structural control of solids is the problem of discontinuity‐like defects diagnostics. The main drawback of conventional linear diagnostic methods is the complicated differentiation between a weak ‘‘useful’’ signal originated due to a crack and the waves scattered by other inhomogeneities of the material, which are not interesting from the viewpoint of flaw detection. In view of this problem, new acoustic diagnostic methods based on measuring nonlinear acoustic characteristics have recently begun to attract the attention of researchers. The effect of acoustic waves scattering nonlinearly from a thin discontinuity‐like defect in a solid is analyzed. The defect is considered as the interface between two surfaces covered with bulges characterized by different initial deformation. It is shown that the nonlinear scattering into combinational‐frequency waves is much more sensitive to the loading of the interface contacts compared with the scattering into the wave of fundamental ...