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The article reviews the capacities of the acoustic emission method usage to assess the technical condition and integrity of thick-walled welded structures, the quality control of welded joints in multilayer welding. As a result of the analysis of AE control data, the authors propose a set of informative parameters of the AE method, which form a criterion space for separating the reflected signals from defects and signals from interference. [ABSTRACT FROM AUTHOR]

The paper analyzes the acoustic emission signals recorded in several places of the sodium hydroxide outflow from the pipeline during manometric control of its tightness directly during operation. On the basis of the obtained results, a parametric image of the source generating acoustic emission at the sodium hydroxide leak locations was established and an assumption was made about its physical nature. Recommendations are given for selecting criteria to assess the hazard class of an acoustic emission source of this type, and the error of its localization using linear antenna groups is estimated. Since the experimental data were obtained by an industrial acoustic emission control system with low-frequency converters, it is possible to directly transfer the obtained results to industrial leak resistance control of extended objects with sodium hydroxide using the acoustic emission method. [ABSTRACT FROM AUTHOR]

Equations that describe elastic wave propagation in a fracturing solid are obtained. It is shown that a solution to an equation for the velocity potential of longitudinal waves of acoustic emission can be represented as the superposition of the fields of an ensemble of radiating cavities known as monopoles. The monopole ensemble parameters are selected so as the structural characteristics of a medium with cavities barely differ from those of a solid. [ABSTRACT FROM AUTHOR]

The method of diagnosing various constructions of tribosystems by acoustic emission method is developed in the work. The development of the methodology is based on the following assumptions. The activity of acoustic emission during the operation of the tribosystem will depend on the rate of deformation of materials on the spots of actual contact. The total acoustic signal from the friction zone is formed as a result of the interference of the primary acoustic signals from the spots of actual contact with the friction surface, which correspond to the coherence condition. Based on these assumptions, the expression for calculating the informative frequencies that will be generated by the tribosystem in the process. The method of diagnosis contains the following steps: determination of informative frequencies on which it is necessary to register amplitudes; determining the magnitude of the amplitudes that carry the maximum information; distribution of the general acoustic signal on clusters and establishment of functional communication of values of a peak factor of clusters with values of coefficient of friction, speed of wear and time of running-in of tribosystems in an online mode. The use of the developed technique will increase the robustness of the method of diagnosing tribosystems and identify surface processes during wear. [ABSTRACT FROM AUTHOR]

A continuum model is proposed and a system of equations is constructed to describe the processes of destruction of a solid. In the framework of the model, a decaying solid is considered as a heterogeneous medium consisting of two phases—solid and gaseous. Based on the analysis of the energy balance equation, in which its surface component is taken into account, the regularities of the onset of individual stages of the development of the process of destruction of a solid are studied. A description of each of the stages is given, the conditions are investigated, and criteria are formulated under which their implementation is possible. [ABSTRACT FROM AUTHOR]

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A model of disk-like cracks based on amplitude-frequency spectra of acoustic emission, detected in the fracture of a concrete sample, is used to restore their size distribution function, as well as corresponding distributions of porosity and specific area of internal surface of the material. Changes in these characteristics of a solid in a time interval between the instances of detection of the spectra are studied. [ABSTRACT FROM AUTHOR]

Nature of the defects in solid samples generated under the surface irradiation by a pulse of a CO2-laser is investigated by the method of acousti©emission analysis. The laser pulse energy of 1.5 J was insufficient for destroying the sample. The samples were rods made from crystal (aluminum, copper) or amorphous (glass) materials. Acoustic emission signals from a rod face were studied which arise under the action of the laser radiation focused onto the opposite face of the rod. Analysis of data obtained shows that local structural changes arise in all the samples investigated. Defects in the form of microscopic cracks have been generated, and in the case of glass (the most fragile material), the cracks existing prior to irradiation have been developed. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) caused by a stress wave in solid material samples with various thermophysical properties, i.e., copper, aluminum, and glass upon exposure to СO laser pulses is studied. It is found that the general AE picture (the AE signal arrival time, its amplitude, and others) is not reproduced during repeated experiments following one after another, which indicates irreversible local changes occurred in the material structure. The effect of the critical material energy density on the AE pattern during the laser exposure is demonstrated. [ABSTRACT FROM AUTHOR]

The paper demonstrates that during triaxial loading of a core sample of dry sandstone, genetically related frequency ranges form in the waveguide, which are significantly spatially separated, but have a similar dynamics. This is explained by the authors' previously suggested model for the generation of a low-frequency branch of seismic emission as a result of amplitude instability of the seismic envelopes of acoustic oscillations in a structurally inhomogeneous medium. [ABSTRACT FROM AUTHOR]

A quantitative physical model is proposed to describe acoustic emission processes. A technique is developed to reconstruct the structural characteristics of a material from its amplitude-frequency spectrum. Based on the obtained results, the experimental data are quantitatively interpreted using observations of acoustic emission signals during the destruction of a concrete sample. [ABSTRACT FROM AUTHOR]

The basic problems of the acoustic-emission method of nondestructive testing are analyzed. Comparative estimation of the effectiveness of the parameters of acoustic emission signals is performed. It is demonstrated that the methods of analysis are inadequate in a narrow frequency band. The need for the use of methods of spectral analysis for the purpose of increasing the precision and reliability of results is demonstrated. [ABSTRACT FROM AUTHOR]

The scaling of the amplitude and time distributions of acoustic emission pulses, which reflects the self-similarity of defect structures, is revealed. The possibility of separation of independent contributions to the flow of acoustic emission events, which have substantially different scaling exponents, is shown for porous materials. The differences in the scaling exponents are related to the development of plastic deformation and fracture of the materials. The developed approach to an analysis of acoustic emission can be used to describe its predominant mechanisms during deformation. [ABSTRACT FROM AUTHOR]

It was established experimentally that during SHS, reaction systems (Ni-Al, Ti-B, Mo-B, etc.) generated acoustic oscillations in the frequency range from 5 Hz to 1.1 MHz with a pulse power of up to 17 W. It was found that the combustion of different systems is characterized by an individual set of dynamic parameters of acoustic emission in the modes of low ordered discrete pulses and highly ordered self-oscillations. It is shown that the spatial zone of acoustic emission is localized near the combustion wave. Analysis of the acoustic emission mechanisms of SHS is performed. [ABSTRACT FROM AUTHOR]

A method has been developed for producing a sharp crack and evaluating the fracture toughness characteristics of ceramic materials from the acoustic emission parameters. The method involves the use of a computer-aided measuring and control system and the appropriate FAE 1.0 software. With this method, it is possible to determine the important characteristics of the fracture toughness of ceramics, such as the R-curve for a fixed crack growth rate and V − K-diagram in a wide range of subcritical crack growth rates. [ABSTRACT FROM AUTHOR]

The effect of preliminary ultrasound action on the mechanical properties and features of the structure of zirconium-based bulk metallic glasses has been studied by the method of acoustic emission under uniaxial compression. Results of studies have been interpreted using the polycluster model of the structure of amorphous metallic alloys. Analysis of the obtained data has allowed us to substantiate the mechanism of the change in the structure and strength of metallic glasses as a result of alternating-sign mechanical loading with an ultrasound frequency of 20 kHz. [ABSTRACT FROM AUTHOR]

The dynamics of the first deformation bands in an aluminum-magnesium A5456 alloy deformed at a constant rate of increase of stresses $$\left( {\dot \sigma _0 = const} \right)$$ is studied by acoustic emission and simultaneous high-speed video filming. A linear relation is found between an acoustic signal and the area of the first band during the first 20 ms of its development. Acoustic precursors are shown to be used to trigger devices with a positive or negative feedback to amplify or suppress deformation jumps, respectively. [ABSTRACT FROM AUTHOR]

It has been revealed that replacing a rough copper powder with a nanopowder increases the acoustic emission (AE) upon sintering the pressings of the W + 20% Cu structure. Hydrogen sintering of the W + 20% Ag structure is accompanied by an elevated level of acoustic emission when compared to vacuum. At the same time, the frequency spectra of hydrogen and vacuum processes are similar. For the binary powder systems with an infusible base, the AE after the crystallization of a fusible component has been explained by the relaxation of the internal mechanical stresses which emerge in the material upon cooling. [ABSTRACT FROM AUTHOR]

The paper addresses the dependence of acoustic emission produced in rolled hafnium GFÉ-1 under tensile deformation on the material's structural state. A correlation has been established between the material structure, the level of mechanical properties and the values of acoustic parameters. Acoustic emission in non-recrystallized hafnium under tensile deformation is recorded only at the stages that precede fracture. Upon recrystallization annealing at temperatures of 1123 and 1373 K acoustic emission occurs at all the stages of tensile deformation. The highest level of acoustic emission activity in hafnium is observed during the transition from elastic to elastic-plastic strain. [ABSTRACT FROM AUTHOR]

laboratory system for recording and analyzing acoustic emission was designed and experimentally investigated (tested). A block diagram and the operation algorithm of the system are presented. The relationship between the results of low-frequency, high-frequency, and statistical processing of recorded data and the physical features of input signals is shown using as an example simulated acoustic signals in the various units of the designed system. The system was tested on real test objects in the case of three-point bending of nitrided steel specimens with various thicknesses of the hardened surface layer. It is shown that crack formation leads to emission of signals with an amplitudes of up to 4 V, whereas during deformation in the absence of pronounced cracking, the amplitude of the amplified signal does not exceed 0.5 V. [ABSTRACT FROM AUTHOR]

The early stages of development of Lüders band in recrystallized 5456 alloy have been investigated by the method of acoustic emission and synchronously by high-speed video tapping with a rate of 500 frames/s. It is established that the first acoustic pulse indicates the instant that the first band of localized deformation nucleates (which initiates the formation of the complex structure of the Lüders front) and is in this context an acoustic precursor to the loss of deformation stability of the alloy. [ABSTRACT FROM AUTHOR]

The regularities and mechanisms of acoustic emission in gypseous rocks under heating are considered. Experimental data are interpreted by the thermal gravimetrical and differential thermal analyses. The applicability of thermoacoustic effects to identifying gypseous rocks and evaluating percentage of different minerals in them is verified. [ABSTRACT FROM AUTHOR]

A device is described for comparative evaluation of the thermal shock resistance of ceramic specimens of identical shape and dimensions by recording acoustic emission (AE) pulses during air cooling from 1000C. The number of AE pulses in a unit of time, whose intensity exceeds the 10% level of maximum signal intensity, is used as a comparative characteristic for thermal shock resistance of ceramic materials. Comparison of the AE pulse distribution with respect to amplitude contains additional information about the thermal shock resistance of comparable specimens. With use of high-temperature furnaces with a considerable working volume and treatment of repeated cooling conditions the measurement part of the device may be used for evaluating the comparative thermal shock resistance of ceramic specimens and objects of any shape and size during cooling from above 1000°C. [ABSTRACT FROM AUTHOR]

The capabilities of different approaches to the measurement of the inhomogeneity of structures, plasticity, and toughness for problems related to certification of structural steels and establishing the structural mechanisms of failure are compared. [ABSTRACT FROM AUTHOR]

The search urgency of new non-destructive control methods for responsible constructions is proved. An acoustic-emission responsible structures control method is suggested which is based on invariants method and Mann-Whitney U-criterion. A generalization of analytical relations for invariants method is performed. A device for estimating the constructions destruction processes during acoustic-emission control using invariants method is described. [ABSTRACT FROM AUTHOR]

The monitoring of pneumatic cylinders is relevant in two fields – pneumatic cylinder operation monitoring and energy saving. One important problem is the detection of air leakage. Typically, leakage occurs between the pneumatic cylinder housing and the piston. Air flow through the leaks generates acoustic emission. In this case, acoustic emission is generated inside the object when the pneumatic cylinder operates. The working principle of the investigated method is based on measurement of acoustic emission (30 kHz – 200 kHz) on the pneumatic cylinder housing and inside the pneumatic cylinder, and measurements of the force of the pneumatic cylinder. The proposed non-destructive method may be used for the diagnostics of working pneumatic cylinders. [ABSTRACT FROM AUTHOR]

The optical systems operating under great ambient temperature drops use materials with special properties, e.g., with invariable geometric characteristics, such as Zerodur glass ceramic with zero coefficient of thermal expansion. Strong precision joints of parts are necessary elements of systems. Fracture processes in loaded materials are studied by the method of acoustic emission, which allows one to record the instant of crack initiation and to study crack development in a brittle material during loading. The evaluation of the strength of brittle optical materials and their nanojoints by the method of acoustic emission has been shown to have good prospects. It has been found that the number of acoustic emission pulses depends on specimen strength. In tests of nanojoints of pyroceramics, two characteristic fracture modes are possible: with crack propagation into the specimen material and without crack propagation beyond the seam limits. The method of acoustic emission assures reliable recording of these fracture modes. [ABSTRACT FROM AUTHOR]

A phenomenological model for emission responses of a geophysical medium is proposed for the description of the general variation patterns of seismic and acoustic emission signals from rock masses and loaded samples. In this model, based on simplified equations, the responses of the medium to pulsed vibrational and electric fields are examined together with the relaxation process; in the simplest particular case, the latter can be described by the Omori law. [ABSTRACT FROM AUTHOR]

The informative parameters and the behavior of the acoustic emission that accompanies the deformation and fracture of rock samples under various conditions of mechanical loading, thermal action, and humidification are considered. The main directions of the development of models for the acoustic emission in geological materials are analyzed. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The change in the spatial distribution of acoustic emission sources in the course of the deformation and fracture of samples of materials and rocks is accompanied by changes in the amplitude distribution of the received signals because of the geometric spread of the elastic wave front. It is customary to characterize the amplitude distributions of acoustic emission signals in terms of the b value (the slope of the differential amplitude distribution). In particular, the localization of the sources may cause a decrease in the b value, which is usually interpreted as a precursor of macrofracture. A correct interpretation of the decrease in the b value is only possible if the location of the sources in space is accomplished and a correction for the spread and attenuation of elastic waves is introduced. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The dependence of the spectral position of the electroluminescence bands of epitaxial light‐emitting diode n+–n–p structures (GaAs0.15P0.85) on the density of a direct heterojunction current at different successive instants of time — before an acoustic emission and after it — has been revealed. The shifts of the electroluminescence bands accompanied by acoustic emission can be divided into three types according to the density of the current: (1) short‐term shifts due to relaxation of the defect structure of a sample — at relatively low currents, (2) the magnitude of the reverse shift being determined by the current density — at large currents, and (3) formation of an IR band (1.5–1.1 eV) with irreversible degradation changing in the red (1.75 eV) and green (2.19 eV) bands of the electroluminescence spectrum — at ultrahigh currents (∼100–200 A/cm2). [ABSTRACT FROM AUTHOR]

We give a review of works devoted to the application of the acoustic emission method for studying the onset of plastic deformations in crystalline bodies. The mechanisms of generation of acoustic emission signals in the course of plastic deformation of various materials are considered. We also illustrate the application of parameters that are used most often and show the trends of development of investigations in this field. [ABSTRACT FROM AUTHOR]

The Kaiser effect was observed in the measurement of acoustic emission (AE) during the course of uniaxial compression of the bulk samples of metallic glasses Zr[sub 41]Ti[sub 14]Cu[sub 12.5]Ni[sub 10]Be[sub 22.5] and Zr[sub 52.5]Ti[sub 5]Cu[sub 17.9]Ni[sub 14.6]Be[sub 22.5]. The field-ion microscopy study of bulk Zr[sub 41]Ti[sub 14]Cu[sub 12.5]Ni[sub 10]Be[sub 22.5] shows that this glass has a polycluster structure. This fact allows one to reveal the nature of AE appearing during the course of deformation of metallic glasses and to interpret the observed Kaiser effect. The dislocations generated at the intercluster boundaries and moving through the glass bulk are the sources of AE. © 2002 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

We advance a hypothesis on the correlation of the total count of acoustic-emission signals and the acoustic-emission measure of damage of crystalline solids with the level of their true strain. This hypothesis is corroborated by the results of our investigations and data from the literature for different types of mono- and polycrystalline solids. We show that the dependence of the sum of amplitudes of acoustic-emission signals and the acoustic-emission measure of volume damage of these materials on their true tensile or compressive strain can be described by a linear function as the first approximation. [ABSTRACT FROM AUTHOR]

Using the acoustic emission method, we study deformation processes in a plastic structural material with different technological inheritance properties under static and cyclic loading condition. The dependence of the total acoustic emission on applied stresses is shown to contain a special point characterizing the moment of change in the stress-strain state of the surface layer of the material. We derive relationships for the evaluation of fatigue limits of structural materials by acoustic emission inspection results. [ABSTRACT FROM AUTHOR]