RU2775204C1 - Method for determining the coordinates of defects during acoustic emission control - Google Patents

Abstract

FIELD: quality control.

SUBSTANCE: invention relates to non-destructive testing of metal structures by acoustic emission method and can be used to determine the coordinates of defects in extended and large-sized objects of the railway, aviation, space, oil and gas industries with limited access to them. The essence lies in the fact that at least three acoustic emission transducers are installed on the controlled product, at a distance between the centers of the transducers in a group not exceeding the minimum acoustic wave length, the product is loaded, acoustic emission signals generated by the defect of the product are received, the phase difference between the signals registered by the transducers is determined in the group for each signal which determines the angle characterizing the direction of wave propagation, while determining the distance to the defect by the time of the rise of the leading edge of the wave, and the coordinates of the defect are determined by certain mathematical expressions.

EFFECT: determination of the coordinates of the AE source using a minimum number of receiving transducers with limited access to the object of control while maintaining the accuracy of the location of defects.

1 cl, 3 dwg, 2 tbl

Description

The invention relates to non-destructive testing of metal structures by the method of acoustic emission and can be used to determine the coordinates of defects in extended and large-sized objects of the railway, aviation, space, oil and gas industries with limited access to them.

There is a known method for determining the coordinates of sources of acoustic emission signals (see patent RU No. 2356043 dated June 27, 2007), including installing n acoustic transducers on structures, determining the propagation velocity of acoustic emission signals on structures and the difference in their arrival times at acoustic transducers, calculating coordinates from them of the source of acoustic emission signals, an acoustic transducer of the simulator is installed in the zone limited by the piezoantenna, and the calculation of the arrival times of acoustic emission signals to the acoustic transducers that make up the piezoantenna is carried out using the signals filtered using wavelet filtering, the error in determining the coordinates of the acoustic transducer of the simulator is calculated, the threshold values are selected amplitude values of the coefficients for wavelet filtering, at which the error in determining the coordinates of the acoustic transducer of the simulator takes a minimum value, the frequency range changes wavelet filtering zone until the error in determining the coordinates of the simulator acoustic transducer takes the minimum value, after which the metal structure is loaded, and the acoustic emission signals are filtered and their coordinates are determined using the obtained wavelet filtering parameters.

The disadvantage of this method is that the coordinates of the signal source are determined by the difference in the times of their arrival at the acoustic transducers, that is, it is necessary to use several transducers that make up the piezoantenna, which is a limiting factor in the control of extended objects.

The closest to the proposed solution is the method of locating defects during acoustic emission control (see patent RU No. 2586087 dated 30.03.2015), which consists in the fact that acoustic emission transducers are installed on the controlled product, the product is loaded, acoustic emission signals generated by the defect are received products, acoustic emission transducers are installed on the test object in groups of at least three in each, at a distance between the centers of the transducers in the group not exceeding the minimum acoustic wavelength, in each group, for each signal, the phase difference between the signals recorded by the transducers is determined, by which the angles are determined characterizing the directions of wave propagation relative to each group of transducers, and the coordinates of defects are determined by the formulas:

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

The disadvantage of the method adopted for the prototype are the limitations associated with the need to install two groups of sensors on the control object, which is not always possible with limited access to it, for example, a protective cover.

The main objective of the invention is to determine the coordinates of the AE source using the minimum number of receiving transducers with limited access to the control object.

The problem is solved due to the fact that in the proposed method for determining the coordinates of defects during acoustic emission control, which consists in the fact that at least three acoustic emission transducers are installed on the controlled product at a distance between the transducer centers in a group not exceeding the minimum acoustic wavelength , the product is loaded, the acoustic emission signals generated by the defect of the product are received, a group of acoustic emission transducers of at least three is installed on the test object, in the group for each signal the phase difference between the signals recorded by the transducers is determined, by which the angle characterizing the direction of wave propagation is determined, at In this case, only one group of acoustic emission transducers is installed on the product and the distance to the defect is determined by the rise time of the leading wave front, and the coordinates of the defect are determined by the formulas

x _d \u003d l⋅cosα ₁ ,

y _d \u003d l⋅sinα ₁ ,

where l is the distance from the group of transducers to the defect, mm,

sinα ₁ and cosα ₁ - sine and cosine of the angle of the wave propagation direction in the transducer group.

On FIG. 1 is a graph of the waveform versus time. On FIG. Figure 2 shows a graph of the rise time of the wave front as a function of the distance from the source to the receiving transducer. On FIG. 3 shows the layout of a group of acoustic emission transducers.

The method is implemented as follows.

At least three acoustic emission transducers are installed on the controlled product at a distance between the centers of the transducers not exceeding the minimum acoustic wave length, in the group for each signal the phase difference between the signals recorded by the transducers is determined, by which the angle characterizing the direction of wave propagation is determined by the formula:

where ϕ ₂₁ - the phase difference of the signals on the transducers 2 and 1; ϕ ₃₁ - the phase difference of the signals on the transducers 3 and 1; then the product is loaded, the acoustic emission signals generated by the defect of the product are received, and the distance to the defect is determined from the rise time of the leading wave front, and the coordinates of the defect are determined by the formulas:

where l is the distance from the transducer group to the defect, mm;

sinα ₁ and cosα ₁ - sine and cosine of the angle of the wave propagation direction in the transducer group.

Example 1

Experimental studies were carried out on a pressure vessel made of steel 20 and having dimensions: length 1150 mm, bottom diameter 219 mm, bottom thickness 45 mm, shell wall thickness 5 mm.

Prior to the beginning of the control, the rise time of the leading wave front was experimentally determined depending on the distance on the sample, which has a shape and material similar to the controlled object. To do this, at a known distance from the transducers, an acoustic wave was created using a Su-Nielsen simulator (pencil break) and recorded by receiving transducers.

Then, a series of experiments simulating the growth of a crack was carried out on the object under study. Acoustic emission transducers were installed on the vessel, the sensitivity of which was calibrated using a Su-Nielsen simulator (pencil break). The data are shown in table 1.

Then built the experimental dependence of the rise time of the leading edge of the wave from the distance from the source to the receiving transducer (see Fig. 2).

After that, the vessel was hydraulically loaded to a maximum pressure of 10 MPa using a pumping station at a speed of 3-5 MPa/min and the signals were recorded by the acoustic emission system STsAD 16.03 (certificate RU.C.27.007.A No. 39729, registered in the State Register of Measuring Instruments No. 18892-10). The signals registered by the transducers are transmitted to a computer, where the graphs of the waveforms versus time are plotted. The computer implements an algorithm for determining the phase difference in a group of converters using the correlation function by the position of the maximum of the signal correlation function. From the transducers of the group, the phase difference between transducers 2 and 1, 3 and 1 was determined, which amounted to: ϕ ₂₁ =0 rad, ϕ ₃₁ =1.4⋅π rad. The experimentally determined phase differences are given in Table. 1. Next, the computer in each group of transducers calculates the value of the wave propagation angle α ₁ (data in table 1) according to formula 1.

According to the graph, the rise time of the leading edge of the wave was determined (see Fig. 1). The rise time of the leading edge of the wave was determined from the difference between the time when the peak in amplitude occurred and the time when the oscillation began:

- полклетки в мкс;

- half cells in µs;

t ₁ \u003d 1100 + 12.5 \u003d 1112.5 μs - the time of the onset of the peak in amplitude;

t ₀ =900+12.5=912.5 μs - the time of the beginning of the oscillation;

t=t ₁ -t ₀ \u003d 1112.5-912.5 \u003d 200 μs - the rise time of the leading edge of the wave.

From the experimental dependence of the rise time of the leading wave front on the distance from the source to the receiving transducer (obtained by calibrating the sensitivity of the channels), the distance from the transducer to the defect was found (see Fig. 2).

After that, according to the group of acoustic emission transducers placed on the object (see Fig. 3), the coordinates of the defect x _d and y _d are calculated in accordance with formulas 2, 3. The data are summarized in Table. one.

The data were processed according to the algorithm contained in the document A02.411709.001 MP “Digital acoustic emission diagnostic systems, modifications SPAD-16.02 and SPAD-16.03. Verification Methodology” (approved by FSUE “SNIIM” on September 12, 2018). The results of data processing are summarized in table. 2.

According to Table. 2, the permissible relative basic error in measuring the coordinates of the defect does not exceed 3%.

Evidence that the determination of the distance from the signal source to the receiving transducer is possible by the rise time of the leading edge of the wave is the calculated R - determination coefficient, which is equal to 0.993 (see Magnus Ya.R., Katyshev P.K., Peresetsky A.A. Econometrics, Initial Course, Moscow, Delo Publishing House, 2004. - 576 pp.) and this makes it possible to use the resulting model to determine any distances to a defect from the rise time of the leading wave front.

R - coefficient of determination (shows the share of variation of the resulting attribute t under the influence of the factor attribute l, is related to the correlation coefficient by a quadratic dependence, in the absence of a connection it is equal to zero, with a functional connection it is one).

l is the distance from the source to the receiving transducer, mm (values are given in Table 1).

t is the rise time of the leading edge of the wave, μs (the values are given in Table 1).

Claims (5)

A method for determining the coordinates of defects in acoustic emission control, which consists in installing a group of acoustic emission transducers on the controlled product at a distance between the centers of the transducers not exceeding the minimum acoustic wavelength, in the group for each signal the phase difference between the signals registered by the transducers is determined, by which the angle characterizing the direction of wave propagation is determined, the product is loaded, the acoustic emission signals generated by the defect of the product are received, characterized in that at least three acoustic emission transducers are installed on the product and the distance to the defect is determined by the rise time of the leading wave front, and the coordinates of the defect determined by the formulas: x _d =l⋅cosα ₁ ; y _d =l⋅sinα ₁ ; where l is the distance from the transducer group to the defect, mm; sinα ₁ and cosα ₁ - sine and cosine of the angle of the wave propagation direction in the transducer group.

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