RU2586087C1 - Method of locating defects during acoustic-emission control - Google Patents

Abstract

FIELD: control equipment.

SUBSTANCE: invention can be used for location of defects. Invention consists in that on monitored item acoustic emission converters are installed, article is loaded, receiving acoustic emission signals generated by defect product; acoustic emission transducers are installed on control object at least three groups in each, at distance between centres of converters in group that does not exceed minimum length of acoustic wave, in each group for each signal determined phase difference between signals registered converters to determine angles, describing wave propagation direction relative to each group of converters, and coordinates of defects is determined by certain mathematical expressions.

EFFECT: technical result is improved accuracy of locating defects in objects of complex structure with variable thickness, considerable number of welds and process holes.

1 cl, 4 dwg, 2 tbl

Description

The invention relates to non-destructive testing of products by acoustic emission and can be used to determine the coordinates of defects in objects of railway and air transport, chemical, petrochemical, energy and metallurgical industries.

A known method for location of defects, namely, that they measure the difference in the arrival times of signals to two sensors and determine the law of sound attenuation in the object, while in the acoustic emission signals received by the sensors generated by the defects of the product, Lamb wave modes are recorded in the form of a wave packet, after presentation whose frequency and time dependences on the spectrograms single out the energy maxima of the antisymmetric and symmetric modes, by the difference in the time of arrival of the energy maxima at the selected frequencies max determined distance from the emitting source to each of the transducers, and then using the previously set damping law calculated coordinates of defect products (see. Russian patent №2523077 C1, IPC G01N 29/14).

The disadvantage of this method is the limitations associated with the inability to reliably determine the coordinates of defects in objects in which there are welded joints, technological holes, elements of variable thickness and other structural and structural inhomogeneities, because antisymmetric and symmetric modes are transformed, converted from one type to another and, therefore, the energy maxima of antisymmetric and symmetric modes are shifted and distorted.

The closest in technical essence to the claimed method is a method for determining the distance between the source and receiver of acoustic emission signals (see RF patent No. 2397490, IPC G01N 29/14), which consists in the fact that the acoustic emission transducer is installed on the controlled product, the product is loaded, receive acoustic emission signals generated by the defect of the product, and Lamb wave modes are recorded, and the modes are recorded as a wave packet, after which the frequency-time dependence on In the programs, the energy maxima of the antisymmetric and symmetric modes are distinguished, and the distance between the transducer and the acoustic emission source is calculated by the difference in the time of arrival of the energy maxima at the selected frequencies.

The disadvantage of this method is the high error in determining the coordinates of defects associated with the uncertainty of the propagation velocity of two selected Lamb modes of acoustic emission signals in objects with structural and structural inhomogeneities and, accordingly, with anisotropy of acoustic properties and strong dispersion (dependence of speed on the frequency of the acoustic wave).

The main objective of the invention is to increase the accuracy of location of defects in objects of complex design with variable thickness, a significant number of welds and technological holes in which the speed of the acoustic signal is an unstable value, depending on the wave frequency and thickness of the product, and the signals can be transformed from one type to another .

The problem is solved due to the fact that in the method for locating defects in acoustic emission control, which consists in installing acoustic emission transducers on the controlled product, loading the product, receiving acoustic emission signals generated by the product defect, acoustic emission transducers installed on the monitoring object groups of at least three in each at a distance between the centers of the transducers in a group not exceeding the minimum acoustic wavelength determined by the upper Itza strip transmission apparatus and speed asymmetric Lamb wave at this frequency in each group for each signal determines the phase difference between the signals registered transducers which define the angles characterizing the wave propagation direction with respect to each group of transducers, and the coordinates of defects is determined by the formulas

where L is the distance between the groups of converters,

tan (α _I ) is the tangent of the angle of the direction of wave propagation in group I;

tan (α _II ) is the tangent of the angle of the direction of wave propagation in group II;

wherein:

where φ ₂₁ is the phase difference of the signals on the converters 2 and 1;

φ ₃₁ - the phase difference of the signals on the converters 3 and 1;

φ ₅₄ is the phase difference of the signals on the converters 5 and 4;

φ ₆₄ is the phase difference of the signals on the converters 6 and 4.

The technical result of the invention consists in increasing the accuracy of the location of defects due to the absence of the effects of wave transformation on the structural inhomogeneities of the investigated object (welds) _{, the} inconstancy of the propagation velocity of the acoustic wave arising due to the dispersion of the waves when the thickness of the test object is varied, and the amplitude-frequency characteristic of the signal accordingly, the error decreases and the reliability of determining the coordinates of defects increases.

In FIG. 1 shows a layout of two groups of acoustic emission transducers. In FIG. 2 shows the layout of the converters in the group. In FIG. 3 is a graph of the voltage versus converters versus time for the group of converters I with numbers 1, 2, 3. FIG. 4 shows the dependence of the correlation function on the phase shift of signals from converters in group I.

The proposed method is implemented as follows. Controlled product: locomotive brake system pressure vessel with dimensions: length 1200 mm, inner diameter 450 mm, wall thickness 12 mm. A series of experiments simulating crack growth was carried out at the object under study. As a simulator of AE, a scrap of the Su-Nielsen lead was used in accordance with GOST R 52727-2007. Acoustic emission diagnostics. General requirements. Two groups of acoustic emission transducers 1, 2, 3, and 4, 5, 6 of the PPAE type 0.05-0.20 at a distance of 750 mm relative to each other were installed on the product. The speed of the asymmetric Lamb wave in the object is C = 3300 m / s, the upper limit of the passband of the converter is f _max = 200 · 10 ³ Hz. For the selected object of control and the type of transducer, the wavelength was

The distance between the centers of the transducers in the group was set equal to 14 mm (less than the wavelength λ). Then the vessel was loaded with a compressor to a maximum pressure of 20 MPa at a speed of not more than 0.25 MPa / s and signals were recorded by the acoustic emission system SCAD 16.03 (number in the State Register of Measuring Instruments No. 18892-10). The signals registered by converters 1, 2, 3 (see Fig. 3) are transmitted to a computer, which calculates for each defect the phase difference φ ₂₁ and φ ₃₁ between the signals registered by converters 2 and 1, 3 and 1 in group I, and also φ ₅₄ and φ ₆₄ , registered converters 5 and 4, 6 and 4 in group II in accordance with the expressions

where Δ ₁ , Δ ₂ , Δ ₃ , Δ ₄ , Δ ₅ , Δ ₆ are the differences in the path of the acoustic emission signal to the transducers.

The computer implements an algorithm for determining the phase difference in the group of converters using the correlation function by the position of the maximum correlation function of the signals. From the converters of group I (see Fig. 4), the phase difference between the converters 2 and 1, 3 and 1 was determined, which amounted to: φ ₂₁ = 0 rad, φ ₃₁ = 1.4 · π rad. The phase difference in the II group of converters was determined similarly. The experimentally determined phase differences are given in table. 1. Next, the computer in each group of converters calculates the value of the angles of propagation of the wave α _I and α _II in accordance with the expressions

After that, the coordinates of the defects x _D and y _D are calculated, in accordance with the expressions

where L is the distance between the groups of converters.

The results of these calculations are summarized in table 1.

The obtained data were processed using GOST R 8.736-2011. Direct multiple measurements. Methods for processing measurement results. The main provisions. The data are summarized in table. 2.

As can be seen from the table. 2, the total relative error of coordinates relative to the distance between the groups of acoustic emission transducers did not exceed 3%.

The advantage of the proposed method compared to the prototype is that the influence of acoustic characteristics (speed and attenuation) and their variations in the control object on the error in measuring the coordinates of defects is minimal. The coordinates of the defect are determined taking into account the phase difference of the two signals at close (less than the minimum wavelength) located acoustic emission transducers, which made it possible to obtain an error in the localization of defects of not more than 3%. The second advantage is the expansion of the technological capabilities of the acoustic emission method using the proposed method by expanding the range of control objects.

Claims (1)

A method for locating defects in acoustic emission control, namely, that acoustic emission transducers are installed on the controlled product, the product is loaded, acoustic emission signals generated by the product defect are received, characterized in that the acoustic emission transducers are installed on the monitoring object in groups of at least three in each, at a distance between the centers of the transducers in a group not exceeding the minimum acoustic wavelength, in each group for each signal is determined once awn phase between the signals registered transducers which define the angles characterizing the wave propagation direction with respect to each group of transducers, and the coordinates of defects is determined by the formulas

where L is the distance between the groups of converters,
tan (α ₁ ) and tan (α ₁₁ ) are the tangents of the angles of the direction of wave propagation in the groups of transducers.

Images