ON THE ACOUSTIC PARAMETERS OF METAL CONSTRUCTIONWHEN DAMAGE IS ACCUMULATED

In the work with the use of nondestructive control methods, the issues of determining acceptable durability or safe resource are considered. It is shown that the design monitoring procedure can be presented as follows: determines the original state zero zone, where the material of the product was subjected to low operational loads; further, with the use of nondestructive control methods, the acoustic parameter is measured (without disassembling the product)., such as the speed of elastic acoustic waves, nonlinear acoustic parameter, difference of velocities with twofrequency sensing, etc.; acoustic scanning of the product's metal is performed, in areas where there have been significant loads, signoff voltages, leading to an intensive accumulation of damage (the destruction of metal leading to cracks); defined zone “N” where the metal state parameter, for which the value is taken, characterizing the difference of the acoustic parameter (the speed of elastic waves, nonlinear acoustic parameter, the difference in velocity in twofrequency sensing) relative to the same parameter in the zone of zero exceeds the established level. The regularities established in the work linking the presence of plastic deformation with the difference in the delays (velocity) of elastic Rayleigh waves at different sounding frequencies at a fixed base between the emitter and the receiver of elastic waves, as well as the behavior of a nonlinear acoustic parameter during the safe resource time, suggest the possibility of using the observd fact as a principle for controlling the limiting state of the material due to plastic deformations on industrial structures. Based on the proposed approach, an engineering methodology for determining the technical condition of the material of the structures of production facilities is proposed, which allows to establish three stages of operation: the reliable operation mode; the controlled operation mode and the critical operation mode.

About the nonlinear acoustic parameter during deformation of AMG61 alloy

Various acoustic effects are used in the study of deformation processes. Acoustic emission is most often mentioned in such studies, and the effects due to nonlinear properties of a deformable metal are the subject of the present work. These properties of real solids lead to nonlinear acoustic effects of the interaction elastic waves forbidden by the theory of elasticity of a homogeneous isotropic body. The work solves the problem of using the principles of nonlinear acoustics in studying the deformation of AMg61 alloy samples. A surface elastic wave is used to control the alloy condition. The process of the elastic wave propagation in the deformed AMg61 alloy due to nonlinear effects is accompanied by generating the double frequency, both of the longitudinal component of the wave and the shear one, the latter is forbidden by equations of the classical elasticity theory. Excitation and reception in the samples was carried out by piezoelectric converters (PES). A wedge converter with a resonance frequency of 1MHz was used to excite the surfactant. The passing surfactant was recorded by a wedge converter with a resonance frequency of 2 MHz. We justified the control technique of the nonlinear acoustic parameter with respect to amplitudes of the first and second harmonics measured during the whole deformation process. An experimental device has been developed to control the nonlinear acoustic parameter in the process of changing the structural state of the sample metal. The pilot study results of the nonlinear acoustic parameter under Amg61 alloy deformation are given. It is shown that the nonlinear acoustic parameter, as well as the acoustic emission activity, is sensitive to changing mechanisms of the defective structure evolution. The non-linearity jump formation during deformation of alloy AMg61 is recorded, which may indicate adjustment of the metal structure. The presented data demonstrate the increase of acoustic nonlinearity in metal at various deformation stages, both at early stages of elastoplastic deformation and at pre-destruction stage, which can be used as the prognostic criterion.

ACOUSTIC NONLINEARITY OF THE UPPER OCEAN LAYER

Представлены результаты исследований нелинейного акустического параметра воды в верхнем слое океана. Метод измерений основан на использовании параметрической генерации звука на различных разностных частотах при бигармоническом излучении высокочастотной накачки. Измерения нелинейного акустического параметра проводились в различные годы в приповерхностном слое в северо-западной части Тихого океана, в верхнем слое до глубины 100 м в Индийском океане, а также на шельфе Японского моря, в бухте Витязь залива Петра Великого. The results of studies of the nonlinear acoustic parameter of water in the upper layer of the ocean are presented. The measurement method is based on the use of parametric sound generation at different difference frequencies under biharmonic radiation of high-frequency pumping. Measurements of the nonlinear acoustic parameter were carried out in various years in the near-surface layer in the North-Western Pacific Ocean, in the upper layer up to a depth of 100 m in the Indian ocean, as well as on the shelf of the Sea of Japan, in the Vityaz Bay of Peter the Great Bay.

Сдвиговые упругие свойства ВТСП керамики в области перехода в сверхпроводящую фазу

The results of studies of shear elastic properties of a high-temperature superconducting (HTSC) of YBa2Cu3O7 - x ceramics in the vicinity of the phase transition to the superconducting state at at a temperature of 91.3 K, as well as at room temperature of 293 K are presented. For the first time, a local increase in the shear nonlinear acoustic parameter N was investigated. Experimental studies of the linear and nonlinear elastic properties of HTSC ceramics YBa2Cu3O7 - x in the region of the superconducting transition showed that the electronic phase transition has significant influence on its elastic properties. Based on the results of experimental measurements linear and nonlinear elastic parameters were determined both at room temperature and in the region phase transition temperature.

Nondestructive Evaluation of Degraded 2.25Cr-1Mo Steel and Estimation of Nonlinear Acoustic Effect Using Bispectral Analysis

The nonlinear acoustic effect has been considered as an effective tool for the evaluation of material degradation. In this paper, the applicability of the nonlinear acoustic effect using bispectrum analysis to the evaluation of degraded 2.25Cr-1Mo steel is investigated. First, artificial aging was performed to simulate the microstructural degradation in 2.25Cr-1Mo steel arising from long time exposure at 538°C. Second, ultrasonic nonlinear parameter was quantitatively measured by bispectrum and power spectrum. The nonlinear acoustic parameter using bispectrum analysis was found to be clearly sensitive to material degradation.