RU2498293C2 - Method of determining coordinates of acoustic emission source - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: two acoustic emission transducers are placed on an inspected article at a certain distance from each other; the article is loaded; acoustic emission signals generated by a defect on the article are received; Lamb wave modes are recorded in form of a wave packet, after presentation of which a frequency-time curve on spectrograms is used to select energy maxima of antisymmetric and symmetric modes; the difference in time of arrival of energy maxima at selected frequencies is used to determine distance between the transducer and the acoustic emission source, after which the obtained results are used to calculate coordinates of the defect on the article.

EFFECT: high accuracy of locating an acoustic emission source.

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Description

The invention relates to non-destructive testing methods and can be used in the chemical, petrochemical, energy, metallurgical industries, in transport facilities.

A known method of determining the distance between the source and receiver of acoustic emission signals (SV 741142 A1, IPC G01N 29/04, filing date 23.10.1978).

The essence of the known method is as follows. Acoustic emission transducers are installed on the controlled product, the product is loaded, acoustic emission signals generated by the product defect are received on two channels, the time intervals between the moments of appearance of signals in different channels are measured, taking the signals of two selected Lamb wave modes as the moments of appearance of the signals, and the distance between source and receiver for measured intervals and signal propagation velocity.

The disadvantages of this method are the implementation complexity, since each of the two modes of the Lamb wave requires registration of its own converter and a measuring channel, and it is necessary to determine the moment of arrival of each mode and measure the time intervals, i.e. use the threshold signal detection method, which has a large error. In addition, this method involves the use of directional converters, and for this it is necessary to know in advance the direction from which the signal will come. In addition, the propagation velocity of the Lamb wave modes depends on the frequency and two different modes can have the same speed at different or the same frequency. The need to take this into account greatly complicates the task and affects the accuracy of determining the distance.

Closest to the technical nature of the present invention is a method for determining the distance between the transducer and the source of acoustic emission (RU 2397490 C2, IPC G01N 29/14, filing date 07.08.2007), which consists in the fact that on the controlled product, which is a flat the sheet, the acoustic emission transducer is installed, the product is loaded, the acoustic emission signals generated by the defect are received, the Lamb wave modes are recorded in the form of a wave packet, after which the time-frequency The dependence on the spectrograms identifies the energy maxima of the antisymmetric and symmetric modes, 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 that uncertainty arises in determining the position of the acoustic emission source, since the geometrical location of the points (source coordinates) equidistant from this (acoustic emission receiver) is, on a flat sample, a circle of radius equal to the determined distance to the source (Figure 1), and on a cylindrical sample, such as a pipeline, the geometric location of points equidistant from the given along the generatrix surface (Figure 2).

Given the fact that the location range can reach values of the order of tens of meters, the value of information about the distance to the acoustic emission source becomes extremely insignificant, especially in real tests, for example, in pipelines.

The objective of the invention is to improve the accuracy of determining the location of the source of acoustic emission.

The problem is solved in that in the method for determining the distance between the transducer and the acoustic emission source, which consists in the fact that the acoustic emission transducer is installed on the controlled product, the product is loaded, acoustic emission signals generated by the defect are received, Lamb wave modes are recorded in the form of a wave packet, after the representation of which by the time – frequency dependence, the energy maxima of antisymmetric and symmetric modes are distinguished in the spectrograms, and the distance between the transducer and the source of acoustic emission are calculated from the time of arrival of the energy maxima at the selected frequencies. According to the invention, two acoustic emission transducers are installed on the monitored product, the distance from the source to each of the transducers is determined, and then the coordinates of the product defect, the acoustic emission source, are calculated.

The technical result of the invention is expressed as follows. By simultaneously determining the distances from the acoustic emission source to two transducers spaced a certain distance from each other, it becomes possible to determine the coordinates of the acoustic emission source from the measurement data of one acoustic emission pulse, which significantly increases the practical value of the method.

The proposed method is implemented as follows. On the test product - a metal sheet, pipe, etc. install two acoustic emission transducers (PAEs) connected to the measuring channel of the system. The acoustic emission signal generated by a defect in the product or simulated using a Hsu-Nielsen source is recorded by the PAE, an oscilloscope, subjected to continuous wavelet transform and presented in time-frequency coordinates.

Then, the energy maxima of A ₁ (f, t), A ₂ (f, t) -antisymmetric and / or S ₁ (f, t), S ₂ (f, t) - symmetric modes of PAE signals of one and the other are distinguished on the spectrograms, analyzing the time-frequency representations A _i (f, t) and / or S _i (f, t) (i = 1,2) determine the difference T _i in time of arrival of different modes at different or one frequency, or one mode at different frequencies , and the coordinates of the acoustic emission source are calculated by the formulas:

a) for flat samples (Figure 3) - Cartesian coordinates (xy) - according to the difference in time of arrival of the energy maxima of different modes at different or one frequency:

where υ _A , υ _S are the arrival rates of the energy maxima of the antisymmetric and symmetric modes, respectively;

T _{i, AS} is the difference in the arrival time of the energy maxima of the antisymmetric and symmetric modes in the first (i = 1) and second (i = 2) PAEs; a = y _o2 -y _o2 is the distance between the PAE;

to calculate the coordinates according to the difference in time of arrival of the energy maxima of one mode at different frequencies:

where υ _f1 , υ _f2 are the arrival rates of the energy maxima of the symmetric or antisymmetric mode at frequencies f ₁ and f ₂ ;

T _{1, f1-f2} , T _{2, f1-f2} are the differences in the time of arrival of the energy maxima of the symmetric or antisymmetric mode at frequencies f ₁ and f ₂ at the first and second PAEs, respectively;

b) for thin-walled cylindrical samples of radius r - cylindrical coordinates (ρ, z, φ):

where D is the diameter of the cylindrical sample.

The cross section z ₁ = z _{2 of a} cylindrical sample containing a defect is uniquely determined.

The experimental dispersion velocity curves υ _A (f) and υ _S (f) of the Lamb wave modes can be calculated by the finite element method for a specific material and product geometry or determined experimentally by excitation of an acoustic emission pulse by a simulator at a point with known coordinates.

Figure 1 shows the possible position of the acoustic emission source when determining the distance on flat samples using one PAE. The determined distance R satisfies the equation x ² + y ² = R ² in Cartesian coordinates.

D - acoustic emission transducer.

Figure 2 shows the possible position of the acoustic emission source when determining the distance on cylindrical samples using one PAE. The determined distance R satisfies the equation ρ ² φ ² + z ² = R ² in cylindrical coordinates;

ρ = r, where r is the radius of the cylindrical surface.

Figure 3 shows the possible position of the acoustic emission source in the case of using two PAEs on flat samples - these are two points u ₁ and u _{2 of the} plane with Cartesian coordinates.

;

;

;

;

and - the distance between the PAE D ₁ and D ₂ .

Figure 4 shows the possible position of the acoustic emission source in the case of using two PAEs on cylindrical samples - these are two points u ₁ and u _{2 of the} surface with cylindrical coordinates

;

;

;

;

.

.

Figures 5 and 6 show the data for the acoustic emission signal obtained by testing on a copper flat sample.

Acoustic pulses recorded by a piezoelectric acoustic emission receiver and digitized using an analog-to-digital converter are shown at the top of each figure. The pulse sampling frequency is 6.25 MHz.

The lower part of each figure shows the time-frequency representations of each pulse obtained as a result of a continuous wavelet transform.

The calculation data obtained as a result of the wavelet transform, when we performed the calibration measurements of the velocities υ _S and υ _{A of the} symmetric and antisymmetric Lamb waves:

с,

с - времена прихода максимумов симметричной и антисимметричной мод Лэмба на первый ПАЭ D₁,

с,

с - времена прихода максимумов симметричной и антисимметричной волн Лэмба.

from,

c are the arrival times of the maxima of the symmetric and antisymmetric Lamb modes at the first PAE D ₁ ,

from,

c are the arrival times of the maxima of the symmetric and antisymmetric Lamb waves.

Then the velocity values υ _S and υ _{A of the} corresponding modes at a distance of a = 0.5 m between the PAE D ₁ and D ₂ : υ _S = 2854 m / s, υ _A = 2180 m / s, and the desired coordinates of the acoustic emission source: x ₁ = x ₂ = 0, y ₁ = y ₂ = 1.38 m. The error in determining the coordinates did not exceed 10%.

Claims (1)

A method for determining the coordinates of an acoustic emission source, namely, that an acoustic emission transducer is installed on a controlled product, the product is loaded, acoustic emission signals generated by a product defect are received, Lamb wave modes are recorded in the form of a wave packet, after which the frequency-time dependence is presented in spectrograms distinguish 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 ah determine the distance between the transducer and the acoustic emission source, characterized in that on the controlled product at a certain distance from each other two acoustic emission transducers determine the distance from the emission source to each of the transducers, and the coordinates of the product defect are calculated from the results obtained.

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