CN106770669A - Two-dimensional shape imaging detection method of defects based on multi-mode acoustic beam synthetic aperture focusing - Google Patents

Abstract

A defect two-dimensional morphology imaging detection method based on multi-mode acoustic beam synthetic aperture focusing belongs to the field of non-destructive testing technology. This method adopts a phased array ultrasonic detector, a phased array ultrasonic probe and a phased array ultrasonic detection system with an inclined wedge, and uses the electronic scanning function of the phased array ultrasonic detector to implement signal acquisition on the test block to obtain the A-scan signal of each aperture of the phased array ultrasonic probe. According to the different types of mode conversion of each aperture excitation acoustic beam at the interface between the wedge block and the test block, the bottom of the test block and the defect surface, a suitable multi-mode acoustic beam is selected from 8 acoustic beam propagation modes. Based on the SAFT imaging principle and Fermat's theorem, the propagation delay of the multi-mode acoustic beam of each aperture is calculated, and the amplitude superposition processing is performed to obtain the reconstructed SAFT image, thereby completely characterizing the two-dimensional morphological characteristics of the defect. This method can realize the correct identification of volumetric and area defects, and then accurately quantify the length, depth and orientation of the defect, and has a high engineering application value.

Description

Two-dimensional shape imaging detection method of defects based on multi-mode acoustic beam synthetic aperture focusing

technical field

The invention relates to a defect two-dimensional shape imaging detection method based on multi-mode acoustic beam synthetic aperture focusing, which belongs to the technical field of non-destructive detection.

Background technique

The qualitative, quantitative, localization and orientation of defects are the research work that non-destructive testing always pays attention to. Ultrasonic testing technology is widely used in defect detection due to its high detection sensitivity and intuitive display of test results. However, conventional ultrasound detects defects using the echo amplitude and phase features in the A-scan signal, and it is difficult to determine the nature of the defect; conventional phased array ultrasonic technology can realize the imaging detection of defects, but only presents part of the defect morphology characteristics, may cause misjudgment of the nature of defects, deviations in quantification and positioning results, and lead to underestimation of the degree of defect damage.

In order to solve the above problems, domestic and foreign scholars have adopted ultrasonic signal and image processing technology to improve the imaging quality, and strive to present defect feature information more intuitively and comprehensively. For example, the synthetic aperture focusing technique (Synthetic Aperture Focusing Technique, SAFT) uses the aperture of the phased array ultrasonic probe to sequentially transmit and receive the full array signal, which has the advantages of large detection range, high resolution, and high detection signal-to-noise ratio, but it still cannot fully characterize Two-dimensional shape of defects; reverse time migration imaging can be used to obtain defect shape and approximate geometric size information, but the amount of processing and calculation is large, and the calculation efficiency is low, which is not conducive to the defect imaging detection of large-scale components.

Contents of the invention

The present invention provides a defect two-dimensional shape imaging detection method based on multi-mode acoustic beam synthetic aperture focusing. The array electronic scanning function and the inclined wedge are used to collect A-scan signals containing multi-mode conversion information such as defect surface reflection waves. According to Fermat's theorem and SAFT imaging principle, the A-scan signals are time-delayed and amplitude-superimposed, and then can be obtained. A SAFT image that fully characterizes the two-dimensional morphology of the defect.

The technical solution adopted in the present invention is: a defect two-dimensional shape imaging detection method based on multi-mode acoustic beam synthetic aperture focusing, using a detection system composed of a phased array ultrasonic detector, a phased array ultrasonic probe and an inclined wedge, using The phased array electronic scanning module implements A-scan signal acquisition on the tested block. According to the different types of mode conversion of the excitation beams of each aperture at the interface between the wedge and the test block, the bottom of the test block and the surface of the defect, an appropriate multi-mode acoustic beam is selected. Based on the SAFT imaging principle and Fermat's theorem, the position of the refraction point of the multi-mode sound beam at the interface between the wedge and the test block is calculated, and the time delay calculation and amplitude superposition processing are performed on the A-scan signal to obtain the reconstructed SAFT image. To characterize the two-dimensional shape characteristics of the defect, the method adopts the following steps:

(a) Selection of Phased Array Ultrasonic Testing Parameters

Select appropriate phased array ultrasonic testing parameters according to the material, shape and size information of the test block, mainly including phased array ultrasonic probe frequency, probe aperture and aperture spacing, etc.;

(b) A-scan signal acquisition

Based on the selected phased array ultrasonic detection parameters, use the phased array electronic scanning function to collect A-scan signals of each aperture and save them in txt format;

(c) Establishment of coordinate system and grid division of image reconstruction area

Take the position of the tip of the wedge as the origin of the coordinates, the interface between the wedge and the tested block is the x-axis, the depth direction is the y-axis, the front edge of the wedge is the positive direction of the x-axis, and the depth direction of the test block is the positive direction of the y-axis to establish a coordinate system. Divide the inspected area into m×n rectangular grids, and the grid nodes are the image reconstruction points;

(d) Refraction point position solution

The excitation sound beam of each aperture of the phased array ultrasonic probe will be reflected/refracted at the interface between the wedge and the test block, the bottom of the test block and the surface of the defect. Taking the i-th aperture as an example, the sound beam propagation path includes five parts: sound path S _1i is the distance from the aperture of the phased array ultrasonic probe to the first refraction point on the interface between the wedge and the test block (corresponding to the speed of sound c ₁ ); the sound path S _2i is the distance from the first refraction point on the interface to the reflection point on the bottom of the test block (corresponding to The sound velocity is c ₂ ); the sound path S _3i is the distance between the reflection point on the bottom surface and the image reconstruction point (corresponding to the sound velocity c ₃ ); the sound path S _4i is the distance between the image reconstruction point and the second refraction point of the test block and the wedge (corresponding to the sound velocity is c ₄ ); the sound path S _5i is the distance from the second refraction point to the receiving aperture (corresponding to the sound velocity c ₅ ); for the propagating sound paths S _2i , S _3i and S _4i in the tested block, the corresponding sound beam mode It can be a transverse wave or a longitudinal wave, so there are 8 sound beam propagation modes, which are collectively called multi-mode sound beams. In the actual detection, the appropriate multi-mode sound beam is selected according to the detection space range;

Therefore, the total sound duration and sound time are respectively:

S(x _0i )＝S _1i +S _2i +S _3i +S _4i +S _5i (1)

Wherein x _0i is the abscissa of the first refraction point;

Fermat's theorem is satisfied when the shortest sound, then the refraction point x _0i satisfies:

(e) SAFT image reconstruction and defect 2D shape acquisition

Read the saved A-scan signals of each aperture, calculate the relative time delay Δt _i between each group of excitation apertures and image reconstruction points according to the coordinates of the refraction points; based on the SAFT imaging principle, apply delays to the A-scan signals point by point and perform amplitude superposition After processing, the composite signal of each image reconstruction point is obtained as:

In the formula, I(m,n) is the stacked amplitude of the grid point (m,n) in the imaging area, f _i is the A-scan signal obtained by the i-th probe aperture, and N is the number of apertures;

Perform amplitude normalization processing and SAFT image reconstruction on the synthesized signal, and the two-dimensional shape characteristics of the defect can be obtained from the image;

(f) Qualitative identification and quantitative detection of defects

Directly based on the two-dimensional shape characteristics of the defect in the image, it can be qualitatively judged whether it is an area type or a volume type defect; for a volume type defect, read the peak coordinate point of the defect imaging area, and its ordinate is the depth of the defect center, using - The 6dB method can give the defect size; for area-type defects, read the upper and lower coordinate points where the peak value of the defect imaging area drops by 6dB, the Euclidean distance between the two coordinate points is the defect length, and the ordinate is the depth of the two ends of the defect ;According to the coordinates (x _k , y _k ) of the highest amplitude point in the kth row of the image reconstruction point, the orientation angle θ of the area-type defect can be obtained from formula (5):

In the formula, M is the number of image reconstruction points.

The beneficial effects of the present invention are: the defect two-dimensional shape imaging detection method based on the multi-mode acoustic beam synthetic aperture focusing uses the propagation characteristics of the multi-mode sound beam to obtain the reflected echo information of the defect surface, and realize the complete two-dimensional shape of the defect Characterization provides an effective solution for the qualitative identification of volume and area defects, and the accurate quantification of defect length, depth and orientation. At the same time, the algorithm involved in this method can be embedded in the flaw detector to realize automatic real-time imaging, which has high engineering application and promotion value.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawings and examples.

Fig. 1 is a schematic diagram of the ultrasonic detection system used in the present invention.

Figure 2 is a schematic diagram of the test block and defects.

Fig. 3 is a schematic diagram of a coordinate system and a sound beam propagation path established during multi-mode sound beam acquisition.

Figure 4 is a conventional SAFT reconstruction image of Φ1mm horizontal holes with a distance of 5mm in the test block.

Fig. 5 is a conventional SAFT reconstruction image of a 5mm crack in the test block.

Fig. 6 is a multi-mode acoustic beam SAFT reconstruction image of a 5mm-long crack in the test block.

detailed description

The defect two-dimensional shape imaging detection method based on multi-mode acoustic beam synthetic aperture focusing, the ultrasonic detection system used is shown in Figure 1, which includes a phased array ultrasonic detector, a phased array ultrasonic probe, and an inclined plexiglass wedge . The specific detection and processing steps are as follows:

(a) The test block to be tested is a carbon steel test block with a thickness of 40mm. The size of the test block is 200mm×200mm×40mm. A 5mm long crack with a center depth of 30mm and a Φ1mm horizontal crack with a depth of 27.5mm and 32.5mm are processed in the test block. hole, as shown in Figure 2.

(b) Using the M2M phased array ultrasonic detection system, the phased array ultrasonic probe is used together with the wedge to detect the test block. The number of array elements of the phased array ultrasonic probe is 32, the center frequency is 5MHz, and 2 array elements are used as 1 excitation aperture, the aperture size is 10mm×1.2mm. The wedge inclination angle is 26°, the first excitation aperture height of the probe is 8.04mm, the sampling frequency is 100MHz, and the electronic scanning step is 0.6mm.

(c) As shown in Figure 3, a Cartesian coordinate system is established, and the detection area is divided into m×n rectangular grids. Among them, the sound velocity of the longitudinal wave of the wedge is 2330m/s, the sound velocity of the transverse wave of the test block is 3230m/s, and the sound velocity of the longitudinal wave is 5700m/s.

(d) As shown in Figure 4 and Figure 5, it is a conventional SAFT composite image of Φ1mm horizontal holes with a spacing of 5mm and a crack with a length of 5mm. It can be seen that the imaging results of these two types of defects are very close, and it is difficult to correctly distinguish the defect types.

(e) Use the electronic scanning function of the phased array to scan the test block, and obtain the sound beam propagation by 31 TTL (transverse wave-shear wave-longitudinal wave, corresponding to S _2i , S _3i and S _4i in formula (1)). The data set formed by the A-scan signal of the mode is exported in the form of data text.

(f) Based on Fermat's theorem and SAFT imaging principle, the coordinates of the refraction points are solved, and the time delay is applied to the A-scan signal point by point according to formula (4) and the amplitude is superimposed to obtain the reconstructed SAFT image. Figure 6 is a multi-mode acoustic beam SAFT image of a crack with a length of 5 mm. It can be seen from the figure that the defect imaging quality is good, the detection resolution is high, and the overall shape is fully characterized. It can be determined that the defect is an area defect. Statistical calculations show that the quantitative result of the length of the defect is 6.2mm, and the central depth positioning is 29.6mm, which shows that the quantitative and positioning errors of this method are relatively small; the position of the strongest amplitude of each row of pixels near the defect in the SAFT image is linearly simulated Combined, the defect orientation obtained from formula (5) is 2.3°, which shows that the most difficult to detect vertical orientation defect is accurately oriented.

Claims (1)

1. the defect two-dimensional appearance imaging detection method of multi-mode acoustic beam synthetic aperture focusing is based on, it is characterized in that, using by phase The detecting system that control battle array ultrasound measuring instrument, phased array supersonic probe and inclined wedge are constituted, using phased array electronic scanning module A is implemented to tested test block and sweeps signal acquisition；According to each aperture excitation acoustic beam in voussoir and test block interface, test block bottom and defect table The difference of face emergence pattern translation type, selects suitable multi-mode acoustic beam；Based on SAFT image-forming principles and Fermat's theorem, calculate In the refraction point position of voussoir Yu test block interface, signal is swept to A carries out time delay calculating and amplitude superposition to multi-mode acoustic beam Treatment, the SAFT images after being rebuild, so that complete characterization defect two-dimensional appearance feature, methods described uses the following steps：

A () phased array ultrasonic detection parameter is selected

Material, shape and size information according to tested test block choose suitable phased array ultrasonic detection parameter, mainly including phase Control battle array ultrasonic probe frequency, probe aperture and aperture spacing；

B () A sweeps signal acquisition

Based on selected phased array ultrasonic detection parameter, the A for gathering each aperture using phased array electronic scanning function sweeps signal, and Preserved with txt forms；

C () establishment of coordinate system and image reconstruction area grid are divided

With voussoir tip location as the origin of coordinates, voussoir and tested test block interface are x-axis, and depth direction is y-axis, voussoir forward position side To being x-axis forward direction, test block depth direction sets up coordinate system for y-axis forward direction, by tested region division into m × n rectangular mesh, its Grid node is each image reconstruction point；

D () refraction point position solves

The excitation acoustic beam in each aperture of phased array supersonic probe will occur anti-in voussoir and test block interface, test block bottom and blemish surface Penetrate/reflect, by taking i-th aperture as an example, its acoustic beam propagation path includes five parts：Sound path S_1iFor phased array supersonic probe aperture is arrived The distance of voussoir and test block interface first refractive point, the correspondence velocity of sound is c₁；Sound path S_2iIt is interface first refractive point and test block bottom surface The distance of pip, the correspondence velocity of sound is c₂；Sound path S_3iIt is bottom reflection point and the distance of image reconstruction point, correspondence velocity of sound c₃；Sound Journey S_4iIt is image reconstruction point and the distance of test block and the refraction point of voussoir second, the correspondence velocity of sound is c₄；Sound path S_5iIt is the second refraction point To the distance of receiving aperture, correspondence velocity of sound c₅；For the propagation sound path S being detected in test block_2i、S_3iAnd S_4i, corresponding acoustic beam pattern It is shear wave or compressional wave, thus has 8 kinds of acoustic beam propagation patterns, is referred to as multi-mode acoustic beam, it is actually detected middle according to detection space Scope selects suitable multi-mode acoustic beam；

Therefore, it is respectively when total sound path and sound：

S(x_0i)=S_1i+S_2i+S_3i+S_4i+S_5i (1)

$T\left(x_{0i}\right)=\frac{S_{1i}}{c_1}+\frac{S_{2i}}{c_2}+\frac{S_{3i}}{c_3}+\frac{S_{4i}}{c_4}+\frac{S_{5i}}{c_5}---\left(2\right)$

Wherein x_0iIt is first refractive point abscissa；

Fermat's theorem is met during most short sound, then refraction point x_0iMeet：

$\frac{dT\left(x_{0i}\right)}{{\mathrm{dx}}_{0i}}=0---\left(3\right)$

E () SAFT image reconstructions are obtained with defect two-dimensional appearance

Each aperture A of reading and saving sweeps signal, and calculating every group according to refraction point coordinates excites between aperture and image reconstruction point Relative time-delay Δ t_i；Based on SAFT image-forming principles, pointwise is swept signal to A and applies to postpone and carry out amplitude overlap-add procedure, is obtained Composite signal to each image reconstruction point is：

$I(m,n)=\underset{i=1}{\overset{N}{\Σ}}{f}_i(t_i-{\mathrm{\Δt}}_i)---\left(4\right)$

In formula, I (m, n) is the superposition amplitude of imaging region internal net point (m, n), f_iFor the A of i-th probe aperture acquisition sweeps letter Number, N is aperture number；

Amplitude normalized and SAFT image reconstructions are carried out to composite signal, i.e., defect two-dimensional appearance is obtained from image special Levy；

F () Flaw discrimination is recognized and quantitative determination

Direct basis defect two-dimensional appearance feature in the picture, qualitative judgement is area-type or volume flaw；For volume Type defect, reads the peak coordinate point in defect imaging region, and its ordinate is defect center depth, is to be given using -6dB methods Flaw size；For area-type defect, the upper and lower coordinate points that defect imaging plots peak declines 6dB are read, between two coordinate points Euclidean distance be defect length, ordinate is defect two-end-point depth；According to image reconstruction point row k amplitude peak Coordinate (x_k,y_k), the angle of orientation θ of area-type defect is obtained by formula (5)：

$tan\mathrm{\θ}=\frac{M\underset{k=1}{\overset{M}{\Σ}}{x}_k\·y_k-\underset{k=1}{\overset{M}{\Σ}}{x}_k\·\underset{k=1}{\overset{M}{\Σ}}{y}_k}{M\underset{k=1}{\overset{M}{\Σ}}{x_k}^2-{\left(\underset{k=1}{\overset{M}{\Σ}}{x}_k\right)}^2}---\left(5\right)$

In formula, M is image reconstruction point line number.